fix: validate URL scheme in build_github_request (#2449)

* fix: validate URL scheme in build_github_request

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* test: add missing hostname validation test for build_github_request

* fix: update docstring and fix import grouping per Copilot feedback

* fix: sort imports and simplify url validation in build_github_request

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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>