fix: downgrade Gemini CLI to 0.15.0 to suppress deprecation warnings

Explicitly sets the Gemini CLI version to 0.15.0 in the GitHub Action workflow.
Newer versions of the CLI (0.20+) print a deprecation warning for the `--prompt` flag to STDERR, which the GitHub Action captures and fails to parse as JSON, causing the workflow to crash. Downgrading restores compatibility with the `run-gemini-cli` action.

Also configures the model to `gemini-1.5-flash` for efficiency.

Author: google-labs-jules[bot]

.github/workflows/gemini-review.yml

@@ -21,7 +21,7 @@ jobs:
         uses: google-github-actions/run-gemini-cli@main
         with:
           gemini_api_key: ${{ secrets.GEMINI_API_KEY }}
-          gemini_cli_version: '0.20.2'
+          gemini_cli_version: '0.15.0'
           gemini_model: 'gemini-1.5-flash'
           extensions: |
             [
@@ -72,7 +72,7 @@ jobs:
         uses: google-github-actions/run-gemini-cli@main
         with:
           gemini_api_key: ${{ secrets.GEMINI_API_KEY }}
-          gemini_cli_version: '0.20.2'
+          gemini_cli_version: '0.15.0'
           gemini_model: 'gemini-1.5-flash'
           extensions: |
             [