macOS 15 for PETSc workflows

Author: prj-

.github/workflows/full-mpich.yml

@@ -69,7 +69,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        version: [13, 14]
+        version: [13, 14, 15]
         cfg:
         - {opts: --enable-debug}
         - {opts: --enable-optim --enable-generic}

.github/workflows/full-openmpi.yml

@@ -69,7 +69,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        version: [13, 14]
+        version: [13, 14, 15]
         cfg:
         - {opts: --enable-debug}
         - {opts: --enable-optim --enable-generic}