update syntax

Author: parthea

.github/workflows/tests.yaml

@@ -16,7 +16,6 @@ concurrency:
 env:
   SHOWCASE_VERSION: 0.35.0
   PROTOC_VERSION: 3.20.2
-  ALL_PYTHON: '"3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13"'
   # Use Python 3.10 for docs to match the version for the sphinx plugin
   # https://github.com/googleapis/synthtool/pull/1891
   DOCS_PYTHON: "3.10"
@@ -33,7 +32,7 @@ jobs:
     - name: Set up all python
       id: all_python
       run: |
-        all_python=$(echo ${{ vars.ALL_PYTHON }} | jq -Rrc 'split(",")')
+        all_python = ConvertTo-Json @("3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13")
         echo "all_python=$all_python" >> "$GITHUB_OUTPUT"
   docs:
     runs-on: ubuntu-latest