ci: define timeout on macOS

Co-authored-by: Bjorn Neergaard <bjorn@neersighted.com>

.github/workflows/main.yml

@@ -81,7 +81,12 @@ jobs:
 
       - name: Ensure cache is healthy
         if: steps.cache.outputs.cache-hit == 'true'
-        run: timeout 10s poetry run pip --version || rm -rf .venv
+        run: |
+          # `timeout` is not available on macOS, so we define a custom function.
+          [ "$(command -v timeout)" ] || function timeout() { perl -e 'alarm shift; exec @ARGV' "$@"; }
+
+          # Using `timeout` is a safeguard against the Poetry command hanging for some reason.
+          timeout 10s poetry run pip --version || rm -rf .venv
 
       # XXX: https://github.com/pypa/pip/issues/11352 causes random failures -- remove once fixed in a release.
       - name: Upgrade pip on 3.11 for macOS