ci: Build and run on macOS on both x86_64 and arm64

The "macos-latest" runners are arm64 these days, while "macos-13"
is older runners that are x86_64. Keep running tests on both,
for as long as the x86_64 based runners are available.

.github/workflows/build.yaml

@@ -78,7 +78,13 @@ jobs:
       - run: meson test -C builddir -v
 
   macos:
-    runs-on: macos-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        runner:
+          - macos-13 # x86_64
+          - macos-latest # aarch64
+    runs-on: ${{matrix.runner}}
     steps:
       - uses: actions/checkout@v3
       - run: brew install nasm meson
@@ -105,15 +111,6 @@ jobs:
       - run: CFLAGS=-Werror make -j$(nproc) ARCH=aarch64 CC=aarch64-linux-gnu-gcc CXX=aarch64-linux-gnu-g++
       - run: qemu-aarch64 -L /usr/aarch64-linux-gnu/ ./codec_unittest
 
-  macos-cross-arm64:
-    runs-on: macos-latest
-    steps:
-      - uses: actions/checkout@v3
-      - run: make gmp-bootstrap
-      - run: make gtest-bootstrap
-      - run: c++ --version
-      - run: CFLAGS=-Werror make -j$(sysctl -n hw.ncpu) ARCH=arm64
-
   ios-cross-arm64:
     runs-on: macos-latest
     steps: