Bump action versions. (#2591)

I was looking at this due to some warnings about node 12 deprecation. This resolves some of it, where updates are available. We'll probably need to keep half an eye on this for https://github.com/hkusu/review-assign-action/issues/20 and https://github.com/z0al/dependent-issues/issues/535, which haven't been addressed yet.

AFAICT no config versions are needed for these version bumps.

.github/workflows/stale.yaml

@@ -11,7 +11,7 @@ jobs:
   stale:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/stale@v5
+      - uses: actions/stale@v7
         with:
           stale-issue-message: >
             We triage inactive PRs and issues in order to make it easier to find

.github/workflows/sync_repos.yaml

@@ -22,7 +22,7 @@ jobs:
     steps:
       # Checkout our main repository.
       - name: Checkout the main repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       # Run the sync script.
       - name: Sync to other repositories