fix: skip unavailable issue comments endpoint

[johncomar]

Summary

This PR lets the tap handle repositories where GitHub disables the repository-level issue comments endpoint.

GitHub can return "has_issues": false and "has_pull_requests": false in a repository payload. For those repositories, GET /repos/{owner}/{repo}/issues/comments can return 404 Not Found even though the repository itself is readable and other endpoints can still be extracted.

Instead of failing the sync for that case, the tap now skips issue comment extraction for repositories where GitHub explicitly reports that both Issues and Pull Requests are disabled.

This follows the same conservative pattern added for repositories with pull requests disabled in #571.

Behavior

• When has_issues and has_pull_requests are both exactly false, the tap skips the /issues/comments request for that repository.
• When either flag is true, missing, null, 0, or otherwise unknown, behavior is unchanged: the tap still requests /issues/comments and surfaces GitHub errors normally.
• The change applies only to issue comment extraction.

Implementation

• Includes GitHub's has_issues field in repository records.
• Carries that flag to repository child stream context alongside has_pull_requests.
• Checks both flags before requesting /repos/{owner}/{repo}/issues/comments.

Related stream audit

This PR does not broadly gate every issue-adjacent stream.

The issue comments endpoint can include pull request conversation comments because GitHub models pull requests as issues. For that reason, the tap skips only when GitHub explicitly reports that both Issues and Pull Requests are disabled.

The following streams were intentionally left unchanged and continue to delegate normally when has_issues is false:

• issues
• issue_events
• milestones
• labels

The focused change is limited to issue_comments, where the repository-level issue comments endpoint can fail when both Issues and Pull Requests are disabled.

What this does not change

• It does not add broad 404 or 403 tolerance.
• It does not suppress generic GitHub errors.
• It does not change pull request extraction.
• It does not change discussion extraction.

Validation

LOGLEVEL=WARNING uv run pytest tests/test_tap.py -k 'has_issues or issue_comments or issue_capability'
# 16 passed, 18 deselected

uv run --with ruff==0.15.15 ruff check tap_github/repository_streams.py tests/test_tap.py
# All checks passed

uv run mypy tap_github
# Success: no issues found in 12 source files

uv run ty check tap_github
# All checks passed

git diff --check
# passed

[TrishGillett]

Good catch to recognize this stream is valid if either is True!

[stray-nick]

Looks like this follows #571 exactly, but for issues.

Only comment I have is given this is a second occurrence of the same issue, should we extend it to other "potentially-disableable" github artifacts now? cc @TrishGillett