Ensure that the web build is compatible with actions/checkout versions >= 3.1.0

[pichlermarc]

#3321 aims to pin actions/checkout to v3.0.2 in the web builds, as v3.1.0 broke our pipeline.

Our pipeline uses the circleci/node:16-browsers image, which sets the default user to a non-root circleci user. This is an unsupported path according to GitHub Actions documentation. It causes files to be not writable, as they are owned by another user (see actions/checkout#956), thus failing the build on checkout.

#3321 is NOT a permanent solution as we won't be able to update actions/checkout without switching to another image, but it will unblock other PRs with failing builds for now.

For this issue to be considered complete, a permanent solution (such as switching to another image that uses root-user only) needs to be found and implemented.