meson CI: update GCC to 13

Signed-off-by: Rosen Penev <[email protected]>
(cherry picked from commit 0de650d)

Author: neheb

.github/workflows/on_PR_meson.yaml

@@ -12,7 +12,7 @@ jobs:
     name: Linux-GCC${{matrix.cxx}}-deps=${{matrix.deps}}
     strategy:
       matrix:
-        cxx: ['7', '11']
+        cxx: ['7', '13']
         deps: ['forcefallback', 'default']
     steps:
       - uses: actions/checkout@v4