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

The [contributor guide](https://forgejo.org/docs/next/contributor/) contains information that will be helpful to first time contributors. All work and communication must conform to Forgejo's [AI Agreement](https://codeberg.org/forgejo/governance/src/branch/main/AIAgreement.md). There also are a few [conditions for merging Pull Requests in Forgejo repositories](https://codeberg.org/forgejo/governance/src/branch/main/PullRequestsAgreement.md). You are also welcome to join the [Forgejo development chatroom](https://matrix.to/#/#forgejo-development:matrix.org).

### 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>

web_src/js/components/DashboardRepoList.vue

@@ -9,6 +9,7 @@ const {appSubUrl, assetUrlPrefix, pageData} = window.config;
 const commitStatus = {
   pending: {name: 'octicon-dot-fill', color: 'yellow'},
   success: {name: 'octicon-check', color: 'green'},
+  skipped: {name: 'octicon-skip', color: 'grey'},
   error: {name: 'gitea-exclamation', color: 'red'},
   failure: {name: 'octicon-x', color: 'red'},
   warning: {name: 'gitea-exclamation', color: 'yellow'},