Update Python version to 3.9, minimum supported on Ubuntu 24.04. (#7086)

Author: jonsimantov

.github/workflows/update-cpp-sdk-on-release.yml

@@ -53,7 +53,7 @@ jobs:
       - name: Setup python
         uses: actions/setup-python@42375524e23c412d93fb67b49958b491fce71c38 # v5.4.0
         with:
-          python-version: 3.7
+          python-version: 3.9
 
       - name: Check out firebase-cpp-sdk
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2