fix GitHub actions

don't test experimental Python versions (dependencies are missing),
update PETSc to 3.23.x

Author: MarDiehl

.github/workflows/Fortran.yml

@@ -2,7 +2,7 @@ name: Grid and Mesh Solver
 on: [push]
 
 env:
-  PETSC_VERSION: '3.22.2'
+  PETSC_VERSION: '3.23.1'
   HOMEBREW_NO_ANALYTICS: 'ON'     # Make Homebrew installation a little quicker
   HOMEBREW_NO_AUTO_UPDATE: 'ON'
   HOMEBREW_NO_BOTTLE_SOURCE_FALLBACK: 'ON'

.github/workflows/Python.yml

@@ -9,7 +9,7 @@ jobs:
 
     strategy:
       matrix:
-        python-version: ['3.10', '3.11', '3.12', '3.13', '3.13t', '3.14', '3.14t']
+        python-version: ['3.10', '3.11', '3.12', '3.13']
         os: [ubuntu-latest, macos-latest, windows-latest]
       fail-fast: false