mass-rebuild-reporter: Only search for issues in the current repsitory

When looking for the previous issue filed for a mass rebuild, we were
searching through repositories in all of GitHub instead of just
fedora-llvm-team/llvm-snapshots.  This meant that issues filed in forks
would prevent the mass rebuild reporter from filing and issue in the
main repository.

.github/workflows/mass-rebuild-reporter.yml

@@ -34,7 +34,7 @@ jobs:
           result-encoding: string
           script: |
             const issues = await github.rest.search.issuesAndPullRequests({
-              q: "label:mass-rebuild+is:issue",
+              q: "repo:" + process.env.GITHUB_REPOSITORY + "+label:mass-rebuild+is:issue",
               sort: "created",
               order: "desc",
               per_page: 1