fix(gitextractor): disable git auto gc/maintenance while cloning

[DoDiODev]

Summary

Incremental git collection fails sporadically in Collect Commits with:

could not find '/tmp/gitextractorXXXX/objects/pack/.tmp-26800-pack-<sha>.idx' to open: No such file or directory

Root cause: since git 2.29, git fetch ends with git maintenance run --auto
(older versions: git gc --auto), and that runs detached in the background
by default. For an incremental collection GitcliCloner runs several fetches
(shallow fetch, --shallow-since, --deepen rounds). The last one may leave a
background maintenance or gc process repacking the repository while libgit2 is
already scanning objects/pack/. libgit2 sees the temporary
.tmp-<pid>-pack-*.idx file, which git renames or removes a moment later, and
the subtask aborts. Because this is a race, the failure is intermittent.

This PR passes
-c gc.auto=0 -c gc.autoDetach=false -c maintenance.auto=false to every git
command run by GitcliCloner. The clone is a short-lived temporary directory
that is removed after extraction, so automatic housekeeping has no benefit
there. The explicit git repack -d in deepen() is still executed
synchronously as before.

A regression test runs an incremental clone with GIT_TRACE and asserts that
git does not start maintenance run / gc --auto. Without the fix the test
fails with
run_command: git maintenance run --auto --no-quiet --detach after each fetch.

Does this close any open issues?

N/A

Screenshots

N/A

Other Information

• Unknown config keys are ignored by git, so maintenance.auto is safe on git
  versions older than 2.29; gc.auto=0 covers those versions.
• Checked on a local instance (git 2.56.0): before the change an incremental
  run failed in Collect Commits with the error above; with the change, 47
  gitextractor tasks across two further pipeline runs completed without it.
• Full CI mirror on my fork, including unit tests (the new test passes there),
  lint and e2e on MySQL and PostgreSQL:
  run