Open conflicted updates and skip forks

[timkpaine]

Description

Open update pull requests even when generated changes fail git diff --check, while retaining a failed aggregate result. Warn in affected PR bodies, skip fork repositories, and transparently rewrite GitHub SSH template sources through installation-token HTTPS authentication.

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / code cleanup
• CI / build configuration
• Other (describe below)

Checklist

• Linting passes (make lint)
• Tests pass (make test)
• New tests added for new functionality
• Documentation updated (not applicable)
• Changelog / version bump (not applicable)

[github-actions]

Test Results

18 tests  +2   18 ✅ +2   0s ⏱️ ±0s
 1 suites ±0    0 💤 ±0 
 1 files   ±0    0 ❌ ±0 

Results for commit 363ec03. ± Comparison against base commit 2e85ac8.

This pull request removes 1 and adds 3 tests. Note that renamed tests count towards both.

copier_update.tests.test_updater ‑ test_repository_update_stops_when_copier_leaves_conflicts

copier_update.tests.test_github ‑ test_marks_invalid_update_pull_request
copier_update.tests.test_updater ‑ test_counts_conflicted_pull_request_as_updated_and_failed
copier_update.tests.test_updater ‑ test_repository_update_opens_pull_request_when_copier_leaves_conflicts

[codecov]

Codecov Report

❌ Patch coverage is 97.95918% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 84.63%. Comparing base (2e85ac8) to head (363ec03).

Files with missing lines	Patch %	Lines
copier_update/github.py	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #11      +/-   ##
==========================================
+ Coverage   83.21%   84.63%   +1.41%     
==========================================
  Files           8        8              
  Lines         441      475      +34     
  Branches       38       41       +3     
==========================================
+ Hits          367      402      +35     
+ Misses         60       58       -2     
- Partials       14       15       +1     

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