Use macos-12 to keep using Docker (avoid ARM runners)

Github's macos-latest runners now use ARM (M-series) chips, which
don't support nested virtualization. Colima is not even installed
anymore on these machines.
Therefore, to keep using Docker, we need to use macos-12 runners
at most, which still use intel chips.

.github/workflows/build.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-latest]
+        os: [ubuntu-latest, macos-13] # macos-latest uses ARM which doesn't support virtualization
         jdk-version: [21]
     steps:
       - name: Checkout repository

.github/workflows/release.yml

@@ -11,7 +11,7 @@ run-name: "Release ${{ inputs.version }}-(cdp-version)"
 
 jobs:
   release:
-    runs-on: macos-latest
+    runs-on: macos-13  # macos-latest uses ARM which doesn't support virtualization
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4