Minor github actions improvement (#8)

Author: rfay

.github/workflows/tests.yml

@@ -18,6 +18,10 @@ defaults:
   run:
     shell: bash
 
+# This is required for "gautamkrishnar/keepalive-workflow"
+permissions:
+  contents: write
+
 env:
   NIGHTLY_DDEV_PR_URL: "https://nightly.link/ddev/ddev/actions/runs/1720215802/ddev-linux-amd64.zip"
   # Allow ddev get to use a github token to prevent rate limiting by tests
@@ -83,3 +87,4 @@ jobs:
       # keepalive-workflow adds a dummy commit if there's no other action here, keeps
       # GitHub from turning off tests after 60 days
     - uses: gautamkrishnar/keepalive-workflow@v1
+      if: matrix.ddev_version == 'stable'