CI: add py314 to test matrix on GHA

Author: tacaswell

.github/workflows/tests.yml

@@ -73,6 +73,8 @@ jobs:
             pygobject-ver: '<3.52.0'
           - os: ubuntu-24.04
             python-version: '3.12'
+          - os: ubuntu-24.04
+            python-version: '3.14'
           - os: ubuntu-24.04-arm
             python-version: '3.12'
           - os: macos-14  # This runner is on M1 (arm64) chips.
@@ -87,6 +89,10 @@ jobs:
             python-version: '3.13'
             # https://github.com/matplotlib/matplotlib/issues/29732
             pygobject-ver: '<3.52.0'
+          - os: macos-15  # This runner is on M1 (arm64) chips.
+            python-version: '3.14'
+            # https://github.com/matplotlib/matplotlib/issues/29732
+            pygobject-ver: '<3.52.0'
 
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8  # v5.0.0