Fix non-existent branch issues on closed PRs edge case

[GrantBirki]

resolves: #424

[Copilot]

Pull request overview

This PR adds a branch existence check to handle edge cases where deployments are attempted on pull requests with deleted branches (e.g., after merge/close). The fix prevents deployments from failing with unclear errors by proactively checking if the branch exists and providing helpful error messages with alternative deployment options.

Key changes:

• Adds branch existence validation before proceeding with deployments
• Implements conditional logic to skip the check for stable branches, SHA deployments, and forks
• Provides clear, actionable error messages when branches are missing

Reviewed changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/functions/prechecks.js	Adds branch existence check with conditional logic to skip for stable branches, SHA deployments, and forks; includes error handling for 404 and unexpected errors
dist/index.js	Bundled distribution file reflecting the source changes
tests/functions/prechecks.test.js	Comprehensive test coverage for all code paths including success, 404 errors, unexpected errors, and skip conditions

[GrantBirki]