retire macos-12, and add macos-15 to CI

.github/workflows/tests.yml

@@ -21,11 +21,7 @@ jobs:
     strategy:
       matrix:
         # NOTE: build on older OS versions to support older OS versions
-        # macos-14 is m1 mac
-        # macos-13 not used as it doesn't by default have sbt installed.
-        # if macos-12 is updated to 13 SBT needs to be installed before
-        # trying to run it for every workflow using this os.
-        os: [ windows-2019, macos-12, ubuntu-20.04, macos-14 ]
+        os: [ windows-2019, ubuntu-20.04, macos-14, macos-15 ]
       fail-fast: false  # don't immediately fail all other jobs if a single job fails
     name: Native build and test on ${{ matrix.os }} 🦙
     runs-on: ${{ matrix.os }}