Add concurrency to GitHub actions

[pixlwave]

Currently our actions run on the creation of a PR, and then every commit that gets added to the PR. However they stack so that making lots of small commits (e.g. via GitHub's review suggestions) creates a huge queue and slows CI down for everybody. We can add the concurrency parameter along with cancel-in-progress (docs) to the workflows to automatically cancel running tasks when a new one comes in.

Note: As our actions are shared for both PRs and pushing to develop, we should consider whether we also want the same behaviour on develop if multiple PRs are merged into develop quickly.

• Element (Add concurrency to GitHub workflows to auto-cancel older runs. #5101)
• Kit
• SDK (Add concurrency to GitHub Actions. matrix-org/matrix-ios-sdk#1505)