chore: fix release channel detection script

[himanshusinghs]

Proposed changes

The earlier script was not for bash, maybe for windows CMD / Powershell (based on the usage of Write-Output command) so I translated the script to bash in this PR.

Checklist

• I have signed the MongoDB CLA

[Copilot]

Pull Request Overview

This PR converts a PowerShell script to bash for detecting release channels from version strings in a GitHub Actions workflow. The script parses version strings to extract release channel information (latest, alpha, beta, rc) for npm publishing.

• Converts PowerShell regex and string operations to equivalent bash functionality
• Adds explicit shell specification and proper environment variable handling
• Maintains the same logic for extracting release channels from version strings

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[coveralls]

Pull Request Test Coverage Report for Build 17613684857

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 81.29%

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Totals
Change from base Build 17613001615:	0.003%
Covered Lines:	4769
Relevant Lines:	5772

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💛 - Coveralls

[blva]

minor comment

[blva]

LGTM, thanks for the updates