Pin macos CI to version 13

Latest macos environment runs on arm and is thus
incompatible with gcc.

ChangeLog:

	* .github/workflows/ccpp.yml: Pin macos runner
	version.

Signed-off-by: Pierre-Emmanuel Patry <[email protected]>

Author: P-E-P

.github/workflows/ccpp.yml

@@ -253,7 +253,7 @@ jobs:
       CC: clang
       CXX: clang++
 
-    runs-on: macos-latest
+    runs-on: macos-13
 
     steps:
     - uses: actions/checkout@v3