As we have discussed in the past, we should be using the latest version.
This has not been updated in a while.

The comment was originally added in
b3af755254599f474601d0d7b7374dcc36af279a, but
2898c3e0bbf904c68efb194525bcdfeedb3014c2 greatly simplified things
making the previous comment invalid. We no longer need to look at
diffing main versus the PR and whether we are doing a two dot or three
dot diff as we are just diffing the merge commit.

This patch changes getting changed files in the pr code format job to
just checking out the previous two commits (the merge commit and its
porent, the current commit latest in main), which allows us to just diff
the merge commit. This means we do not have to checkout the ref through
the merge base, which should save approximately a minute per job (or
much more in some cases where the PR is particularly out of date).

The tj-actions/changed-files repo has been taken down to the security
incident
(https://www.stepsecurity.io/blog/harden-runner-detection-tj-actions-changed-files-action-is-compromised).

This patch moves these jobs over step-security's fork, which has been
loosely audited and has had the malicious commits removed. This is
mainly intended as a stop-gap to get these actions running again while
we figure out the best path forward.

This patch replaces all instances of ubuntu-latest with ubuntu-24.04
(outside of the entries in libc++) based on the guidelines in the LLVM
CI best practices doc (https://llvm.org/docs/CIBestPractices.html).

This patch haspins all actions in most of the LLVM Github workflows.
This is something we try to do, but no one has gone through and combed
through all of the workflows before this patch.

Notably, this patch does not bump any major versions of actions just in
case there are subtle breaking changes introduced between versions that
could impact us. Also, this patch omits the libc/libc++ workflows so
that they can be split into separate PRs for the respective subproject
maintainers to review.

The version of clang-format we use in the CI to format all PRs is a bit
outdated, leading to some confusion when the CI job produces different
output from what people have locally.

This patch sets the timeout of the code formatting job to 30 minutes.
The job is currently failing in specific circumstances and needs to be
reworked, but as a temp hack, change the timeout to 30 minutes so that
we can catch these jobs before they hit the Github Actions timeout limit
of six hours.

Somewhat (hackily) alleviates #79661 slightly.

Currently the formatter only runs for the main branch, which prevents
the formatter from running for stacked PRs, which have to target user
branches instead of main.