GitHub Actions: Test on Python 3.14 release candidate 2

```diff
- python-version: ["3.10", "3.11", "3.12", "3.13"]
+ python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
```
https://www.python.org/download/pre-releases
https://www.python.org/downloads/release/python-3140rc2

Author: cclauss

.github/workflows/shared.yml

@@ -35,7 +35,7 @@ jobs:
     continue-on-error: true
     strategy:
       matrix:
-        python-version: ["3.10", "3.11", "3.12", "3.13"]
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
         dep-resolution: ["lowest-direct", "highest"]
         os: [ubuntu-latest, windows-latest]