fix: use timestamp of commit instead of updatestamp in get_or_update_branch_head

[joseph-sentry]

Purpose/Motivation

timestamp is the field which we were using before to decide if a commit was to be branch's head or not. The issue with ordering by updatestamp is that updatestamp is nullable which leads to incorrect behaviour where we may pick a commit from very long ago to be the branch head.

What does this PR do?

• order by timestamp descending instead of updatestamp descending

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (226f73d) 95.73% compared to head (390b137) 95.73%.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #356   +/-   ##
=====================================
  Coverage   95.73   95.73           
=====================================
  Files        743     743           
  Lines      16823   16823           
=====================================
  Hits       16104   16104           
  Misses       719     719           

Flag	Coverage Δ
unit	96.05% <ø> (ø)
unit-latest-uploader	96.05% <ø> (ø)

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[codecov-staging]

Codecov Report

All modified and coverable lines are covered by tests ✅

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[codecov-qa]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (226f73d) 96.05% compared to head (390b137) 96.05%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #356   +/-   ##
=======================================
  Coverage   96.05%   96.05%           
=======================================
  Files         628      628           
  Lines       16307    16307           
=======================================
  Hits        15664    15664           
  Misses        643      643           

Flag	Coverage Δ
unit	96.05% <ø> (ø)
unit-latest-uploader	96.05% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
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[codecov-public-qa]

Codecov Report

Merging #356 (390b137) into main (226f73d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #356   +/-   ##
=======================================
  Coverage   96.05%   96.05%           
=======================================
  Files         628      628           
  Lines       16307    16307           
=======================================
  Hits        15664    15664           
  Misses        643      643           

Flag	Coverage Δ
unit	96.05% <ø> (ø)
unit-latest-uploader	96.05% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
utils/temp_branch_fix.py	90.90% <ø> (ø)