ci: fix maintenance branch name pattern

[tzemanovic]

Describe your changes

follow up to #4000 - maintenance branch name should not include patch version

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies:
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.89%. Comparing base (7a0770d) to head (4f5e868).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4008   +/-   ##
=======================================
  Coverage   73.89%   73.89%           
=======================================
  Files         341      341           
  Lines      106451   106451           
=======================================
+ Hits        78657    78661    +4     
+ Misses      27794    27790    -4     

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