fix: Fix 404 not found error for saving approval rules

[robinson96]

save() was getting id of the merge request instead of id of the approval_rule, setting _id_attr to approval_rule_id addresses this issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (48726fd) 96.48% compared to head (e6fb635) 96.48%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2637   +/-   ##
=======================================
  Coverage   96.48%   96.48%           
=======================================
  Files          90       90           
  Lines        5866     5867    +1     
=======================================
+ Hits         5660     5661    +1     
  Misses        206      206           

Flag	Coverage Δ
api_func_v4	82.32% <100.00%> (+<0.01%)	⬆️
cli_func_v4	83.58% <100.00%> (+<0.01%)	⬆️
unit	88.25% <100.00%> (+<0.01%)	⬆️

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

Files	Coverage Δ
gitlab/v4/objects/merge_request_approvals.py	98.76% <100.00%> (+0.01%)	⬆️

[JohnVillalovos]

I'm going to close this as I think it has already been fixed in #2773 . And the latest published version of python-gitlab has the fix.

If you disagree please re-open.