ci: remove build cache from GitHub runners (prevents SIGILL, negligible speedup)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sbryngelson

.github/workflows/test.yml

@@ -98,20 +98,6 @@ jobs:
       - name: Clone
         uses: actions/checkout@v4
 
-      - name: CPU Architecture Hash
-        id:   cpu
-        run: |
-          # Include CPU model in cache key so binaries compiled with -march=native
-          # on one runner aren't reused on a runner with a different ISA (→ SIGILL).
-          arch=$(gcc -march=native -Q --help=target 2>/dev/null | grep -m1 '^\s*-march=' | awk '{print $2}')
-          echo "arch=${arch:-unknown}" >> "$GITHUB_OUTPUT"
-
-      - name: Restore Build Cache
-        uses: actions/cache@v4
-        with:
-          path: build
-          key: mfc-build-${{ matrix.os }}-${{ matrix.mpi }}-${{ matrix.debug }}-${{ matrix.precision }}-${{ matrix.intel }}-${{ steps.cpu.outputs.arch }}-${{ hashFiles('CMakeLists.txt', 'toolchain/dependencies/**', 'toolchain/cmake/**', 'src/**/*.fpp', 'src/**/*.f90') }}
-
       - name: Setup MacOS
         if:   matrix.os == 'macos'
         run:  |