feat: mark skipped checks as skipped (#12606)

A separate commit status is introduced for skipped checks. That enables marking them as such in the UI instead of successful, which could be misleading.

Resolves https://codeberg.org/forgejo/forgejo/issues/10138.

## Checklist

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### Tests for Go changes

(can be removed for JavaScript changes)

- I added test coverage for Go changes...
  - [x] in their respective `*_test.go` for unit tests.
  - [x] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I ran...
  - [x] `make pr-go` before pushing

### Tests for JavaScript changes

(can be removed for Go changes)

- I added test coverage for JavaScript changes...
  - [ ] in `web_src/js/*.test.js` if it can be unit tested.
  - [ ] in `tests/e2e/*.test.e2e.js` if it requires interactions with a live Forgejo server (see also the [developer guide for JavaScript testing](https://codeberg.org/forgejo/forgejo/src/branch/forgejo/tests/e2e/README.md#end-to-end-tests)).

### Documentation

- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.

### Release notes

- [x] This change will be noticed by a Forgejo user or admin (feature, bug fix, performance, etc.). I suggest to include a release note for this change.
- [ ] This change is not visible to a Forgejo user or admin (refactor, dependency upgrade, etc.). I think there is no need to add a release note for this change.

*The decision if the pull request will be shown in the release notes is up to the mergers / release team.*

The content of the `release-notes/<pull request number>.md` file will serve as the basis for the release notes. If the file does not exist, the title of the pull request will be used instead.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/12606
Reviewed-by: Cyborus <cyborus@disroot.org>
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>

modules/structs/commit_status.go

@@ -4,7 +4,7 @@
 package structs
 
 // CommitStatusState holds the state of a CommitStatus
-// It can be "pending", "success", "error", "failure" and "warning"
+// It can be "pending", "success", "error", "failure", "warning", or "skipped"
 type CommitStatusState string
 
 const (
@@ -18,6 +18,8 @@ const (
 	CommitStatusFailure CommitStatusState = "failure"
 	// CommitStatusWarning is for when the CommitStatus is Warning
 	CommitStatusWarning CommitStatusState = "warning"
+	// CommitStatusSkipped is for when the CommitStatus is Skipped
+	CommitStatusSkipped CommitStatusState = "skipped"
 )
 
 var commitStatusPriorities = map[CommitStatusState]int{
@@ -26,6 +28,7 @@ var commitStatusPriorities = map[CommitStatusState]int{
 	CommitStatusWarning: 2,
 	CommitStatusPending: 3,
 	CommitStatusSuccess: 4,
+	CommitStatusSkipped: 5,
 }
 
 func (css CommitStatusState) String() string {
@@ -35,7 +38,7 @@ func (css CommitStatusState) String() string {
 // NoBetterThan returns true if this State is no better than the given State
 // This function only handles the states defined in CommitStatusPriorities
 func (css CommitStatusState) NoBetterThan(css2 CommitStatusState) bool {
-	// NoBetterThan only handles the 5 states above
+	// NoBetterThan only handles the states above
 	if _, exist := commitStatusPriorities[css]; !exist {
 		return false
 	}
@@ -71,3 +74,8 @@ func (css CommitStatusState) IsFailure() bool {
 func (css CommitStatusState) IsWarning() bool {
 	return css == CommitStatusWarning
 }
+
+// IsSkipped returns true if a commit has been skipped.
+func (css CommitStatusState) IsSkipped() bool {
+	return css == CommitStatusSkipped
+}

modules/structs/commit_status_test.go

@@ -18,6 +18,46 @@ func TestNoBetterThan(t *testing.T) {
 		args args
 		want bool
 	}{
+		{
+			name: "skipped is not better than skipped",
+			args: args{
+				css:  CommitStatusSkipped,
+				css2: CommitStatusSkipped,
+			},
+			want: true,
+		},
+		{
+			name: "skipped is not better than success",
+			args: args{
+				css:  CommitStatusSkipped,
+				css2: CommitStatusSuccess,
+			},
+			want: false,
+		},
+		{
+			name: "skipped is not better than pending",
+			args: args{
+				css:  CommitStatusSkipped,
+				css2: CommitStatusPending,
+			},
+			want: false,
+		},
+		{
+			name: "skipped is not better than failure",
+			args: args{
+				css:  CommitStatusSkipped,
+				css2: CommitStatusFailure,
+			},
+			want: false,
+		},
+		{
+			name: "skipped is not better than error",
+			args: args{
+				css:  CommitStatusSkipped,
+				css2: CommitStatusError,
+			},
+			want: false,
+		},
 		{
 			name: "success is no better than success",
 			args: args{