test: support fish deploy hook checks

[Muhtasham]

Changelog

N/A - Testing changes.

Summary

Fixes#462 by making the deploy hook test expectations work when the test process runs with SHELL set to fish.

The stderr hook case now uses redirection syntax that works in fish and POSIX-like shells, and the missing deployer case accepts fish's Unknown command wording in addition to the existing shell-specific messages.

Validation

• PATH="/opt/homebrew/bin:$PATH" SHELL=/opt/homebrew/bin/fish go test ./cmd/platform -count=1
• PATH="/opt/homebrew/bin:$PATH" SHELL=/bin/bash go test ./cmd/platform -count=1
• PATH="/opt/homebrew/bin:$PATH" SHELL=/opt/homebrew/bin/fish go test ./...

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @Muhtasham to sign the Salesforce Inc. Contributor License Agreement.