fix: update existing ruleset when in transition mode

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🐛 Bug: branch-ruleset API crashes if a ruleset already exists (transition mode) #1950
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Previously, blockRepositoryBranchRuleset would always create a ruleset on main with the hardcoded name. This is fine for setup mode but crashes on a duplicate ID creation error in transition mode.

Now, its creations are split between the two modes:

• Setup mode POST creates the ruleset as before
• Transition mode PUT updates the existing ruleset

The PUT update requires a ruleset_id, so I added that as a new option in the Base populated by a new inputFromOctkit.

🎁

[codecov]

Codecov Report

Attention: Patch coverage is 62.50000% with 45 lines in your changes missing coverage. Please review.

Project coverage is 95.42%. Comparing base (211491b) to head (74ef283).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/blocks/blockRepositoryBranchRuleset.ts	48.75%	41 Missing ⚠️
src/base.ts	83.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1951      +/-   ##
==========================================
+ Coverage   95.40%   95.42%   +0.02%     
==========================================
  Files          86       87       +1     
  Lines        3522     3586      +64     
  Branches      201      205       +4     
==========================================
+ Hits         3360     3422      +62     
- Misses        162      164       +2     

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