test(release): select Git Bash explicitly on Windows

[dipeshbabu]

Fixes #206

Summary

• Resolve Git Bash from Git for Windows' own executable directory.
• Invoke that absolute executable for every release-workflow shell test on Windows.
• Add a regression check that verifies the selected shell is a MinGW Git Bash process.

Root cause

The release-automation tests invoked an unqualified bash. When Windows resolved C:\\Windows\\System32\\bash.exe first, the workflow fragments crossed into WSL and lost the Windows command and path environment expected by the test harness.

Impact

Enabling WSL or placing its compatibility executable earlier on PATH no longer causes the release-workflow test suite to select the wrong shell. POSIX test behavior is unchanged.

Validation

• pnpm dlx bun test --timeout 30000 ./tests-ts/release-automation.test.ts --test-name-pattern "uses Git Bash for shell fragments on Windows|executes the manual release cut against all published versions" — 2 passed
• pnpm exec tsc --noEmit
• pnpm exec prettier --check tests-ts/release-automation.test.ts
• git diff --check