build: specify the sha256 hash of the alpine image

[favonia]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.04%. Comparing base (e7286e3) to head (c1b3cc3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1029   +/-   ##
=======================================
  Coverage   95.04%   95.04%           
=======================================
  Files          62       62           
  Lines        3434     3434           
=======================================
  Hits         3264     3264           
  Misses        158      158           
  Partials       12       12           

Flag	Coverage Δ
unittests	95.04% <ø> (ø)

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.