Update actions/setup-go action to v5

Author: renovate[bot]

.github/workflows/pr-auditor.yml

@@ -12,7 +12,7 @@ jobs:
       - uses: actions/checkout@v4
         with:
           repository: 'sourcegraph/pr-auditor'
-      - uses: actions/setup-go@v4
+      - uses: actions/setup-go@v5
         with: { go-version: '1.21' }
 
       - run: './check-pr.sh'