CD: fix release workflow permissions

(Note: v10.3 *was* released successfully,
but the workflow failed to update
the GitHub Releases page at the end
due to token permission problems.)

.github/workflows/release.yml

@@ -21,6 +21,9 @@ jobs:
   release:
     runs-on: ubuntu-20.04
     environment: release
+    permissions:
+      # `gh release` requires write permission on repo contents
+      contents: write
     steps:
       - name: Get code
         uses: actions/checkout@v3