GitHub Actions cache not cleared after composer.json change

[danielmx-dev]

Describe the bug

Recently, a change in the autoload definition inside the composer.json file caused the E2E and Playwright tests to fail due to an issue with the cached dependencies.

Although ideally the ./vendor directory may not be the best place to cache code, the current implementation of https://github.com/Automattic/jetpack-autoloader will create an optimized autoloader map that gets saved to ./vendor/composer. If we update the autoload definition but don't refresh the cache, then we may run into issues when loading classes. Example: p1726855117544489-slack-CGGCLBN58

To Reproduce

1. Perform an update in composer.json
2. Run the E2E tests using a feature branch
3. Perform another update in composer.json
4. Run the E2E tests once again.

Actual behavior

The action will use the cached data, this can be verified in the action logs, in the Setup E2E Environment section.

Cache restored successfully
Cache restored from key: Linux-vendor-<HASH>

Expected behavior

If either composer.json or composer.lock changes, the cache should be ignored. This can be verified in the action logs, in the Setup E2E Environment section.

Cache not found for input keys: Linux-vendor-<HASH>

Additional context

composer-cache definition can be found here: https://github.com/Automattic/woocommerce-payments/blob/develop/.github/actions/e2e/env-setup/action.yml#L28-L33 The issue could be fixed just by adding the hash of the composer.json file to the cache key.