CI: cleanup git submodules in M1 runner

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

.github/workflows/m1_ci.yml

@@ -17,6 +17,14 @@ jobs:
       run:
         shell: "/usr/bin/arch -arch arm64e /bin/bash --noprofile --norc -eo pipefail {0}"
     steps:
+      - name: Clean repository submodules
+        # See https://github.com/actions/checkout/issues/385
+        run: |
+          git submodule deinit .
+          git submodule | cut -c43- | while read -r line; do (git rm "$line"); done
+          git config --local -l | grep submodule | sed -e 's/^\(submodule\.[^.]*\)\(.*\)/\1/g' | while read -r line; do (git config --local --remove-section "$line"); done
+          rm -rf .gitmodules .git/modules
+          git reset --hard HEAD
       - name: Checkout
         uses: actions/checkout@v2
       - name: Setup Zig