[PATCH] GitHub ci(windows): speed up initializing Git for Windows' minimal SDK again

From: Johannes Schindelin <johannes.schindelin@gmx.de>

It used to be the case that initializing the minimal SDK (i.e. a radically slimmed-down subset of Git for Windows' development environment intended to perform the CI builds and little else) took a bit over one minute, would then be cached, and subsequent jobs would take at most half a dozen seconds to initialize said minimal SDK.

It is important that this step is fast because we have to run the test suite in parallel, in a set of matrix jobs, to offset the slowness of the shell-based test suite, and each and every job has to initialize the very same minimal SDK.

While it may sound as if parallelizing the jobs might only waste the generously-provided build minutes but at least the _wallclock_ time would pass quick, in reality it matters a lot: Frequently Git for Windows' or GitGitGadget PRs get stuck waiting for quite a while before CI builds start because other PRs' builds still spend substantial amounts of time to run, blocking due to the concurrency limit being reached.

Since 91839a88277 (ci: create script to set up Git for Windows SDK, 2024-10-09), the situation has worsened: every job that requires the minimal Git for Windows SDK spends roughly two-and-a-half minutes doing so.

With the switch away from the GitHub Action `setup-git-for-windows-sdk`, we incurred more downsides:

- It is no longer possible for said Action to fix problems independently
  from the Git repository, e.g. when new rules about GitHub Actions
  require changes in the way the minimal SDK is initialized.

- The minimal SDK was installed specifically outside of the worktree so
  as not to clutter it nor incur an additional cost to verify that the
  worktree is clean.

Therefore, even if it would be nice to have a shared process between GitHub and GitLab based CI builds, let's switch the GitHub-based CI back to the tried-and-tested `setup-git-for-windows-sdk` Action.

This commit partially reverts 91839a88277 (ci: create script to set up Git for Windows SDK, 2024-10-09).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
    Speed up the Git for Windows SDK initialization again
    
    While waiting for way too many builds in
    https://github.com/gitgitgadget/git/actions to finish, I noticed that
    the minimal Git for Windows SDK initialization now takes a whopping 2.5
    minutes. That's way too much. It used to take a little over a minute
    when uncached, and 2-5 seconds when cached.
    
    Let's fix this regression by reverting to using the
    setup-git-for-windows-sdk GitHub Action (also because that Action will
    soon see another dramatic speed-up, see
    https://github.com/git-for-windows/setup-git-for-windows-sdk/pull/965).

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1841%2Fdscho%2Fci-windows-jobs-speedup-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1841/dscho/ci-windows-jobs-speedup-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1841

 .github/workflows/main.yml | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)