Fix release workflow: add contents:read and Ruby 4.0 smoke test (#51)

Add contents: read permission to the release job — declaring any
permissions block zeros all unlisted ones, so checkout was broken.

Add Ruby 4.0 to the smoke-test matrix to match cross-compile which
already builds for 4.0,3.4,3.3.

Author: ZilvinasKucinskas

.github/workflows/release.yml

@@ -64,7 +64,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ["3.3", "3.4"]
+        ruby: ["3.3", "3.4", "4.0"]
     steps:
       - uses: ruby/setup-ruby@v1
         with:
@@ -87,6 +87,7 @@ jobs:
     runs-on: ubuntu-latest
     if: startsWith(github.ref, 'refs/tags/v')
     permissions:
+      contents: read
       id-token: write
     steps:
       - uses: actions/checkout@v6