ci: build: use the latest x86 macos image available

Upgrade the macos-12 image to macos-13, this is apparently the last x86
osx image that will ever be available on github.

Signed-off-by: Fabio Baltieri <[email protected]>

Author: fabiobaltieri

.github/workflows/build.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-22.04, macos-12, macos-14, windows-2022]
+        os: [ubuntu-22.04, macos-13, macos-14, windows-2022]
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout