Replace canary in CI pipeline

The old canary wasn't available on macOS (ARM64).

```
Runner Image
  Image: macos-14-arm64
  Version: 20250527.1547
```

```
Unknown release: adoptopenjdk-openj9-8.0.252+9.1.openj9-0.20.0
```

Author: joschi

.github/workflows/tests.yml

@@ -35,7 +35,7 @@ jobs:
         GITHUB_API_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       run: |
         . asdf/asdf.sh
-        asdf plugin-test java "$GITHUB_WORKSPACE" --asdf-plugin-gitref "$GITHUB_SHA" --asdf-tool-version adoptopenjdk-openj9-8.0.252+9.1.openj9-0.20.0 java -version
+        asdf plugin-test java "$GITHUB_WORKSPACE" --asdf-plugin-gitref "$GITHUB_SHA" --asdf-tool-version zulu-21.28.85 java -version
     - name: Check update_data.bash
       env:
         GITHUB_API_TOKEN: ${{ secrets.GITHUB_TOKEN }}