ci: Disable macos builds

This needs to be disable until GHA arm-none-eabi-gcc-action is fixed.
See carlosperate/arm-none-eabi-gcc-action#74

Author: sjanc

.github/workflows/build_targets.yml

@@ -27,7 +27,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, windows-latest, macos-latest]
+        os: [ubuntu-latest, windows-latest]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3