chore(api): Improve description for repoCheckCollaborator (#6858)

- Make it clear how the API responds with if the user is a collaborator or not.
- Yes, not ideal. Should've been a JSON response instead - but backwards compatibility.
- Resolves forgejo/forgejo#6837

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6858
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

routers/api/v1/repo/collaborators.go

@@ -82,6 +82,7 @@ func IsCollaborator(ctx *context.APIContext) {
 	// swagger:operation GET /repos/{owner}/{repo}/collaborators/{collaborator} repository repoCheckCollaborator
 	// ---
 	// summary: Check if a user is a collaborator of a repository
+	// description: If the user is a collaborator, return 204. If the user is not a collaborator, return 404.
 	// produces:
 	// - application/json
 	// parameters:

templates/swagger/v1_json.tmpl

@@ -6074,6 +6074,7 @@
     },
     "/repos/{owner}/{repo}/collaborators/{collaborator}": {
       "get": {
+        "description": "If the user is a collaborator, return 204. If the user is not a collaborator, return 404.",
         "produces": [
           "application/json"
         ],