fix(ci): Do not run mac os CI jobs on pull requests

Warpbuild is quite expensive

.github/workflows/qc-mac.yaml

@@ -0,0 +1,31 @@
+name: QC
+on:
+  push:
+    branches: [main]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  checks: write
+  contents: read
+
+jobs:
+  cargo-test:
+    runs-on: warp-macos-13-arm64-6x
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/bin/
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+            target/
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+        # liboqs requires quite a lot of stack memory, thus we adjust
+        # the default stack size picked for new threads (which is used
+        # by `cargo test`) to be _big enough_. Setting it to 8 MiB
+      - run: RUST_MIN_STACK=8388608 cargo test --workspace --all-features