Do not test on macos-12 as the images are not available any more

Author: apolukhin

.github/workflows/ci.yml

@@ -170,7 +170,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-20.04, ubuntu-22.04, macos-12, macos-13, macos-14 ]
+        os: [ ubuntu-20.04, ubuntu-22.04, macos-13, macos-14 ]
         shared: [ OFF, ON ]
 
     runs-on: ${{matrix.os}}