ci: run test-go-pg mise tool install under bash on Windows - #27483

What

Add shell: bash to the Install Go mise tools step in the test-go-pg job so it runs under Git bash on the windows-2022 matrix leg.

Why

test-go-pg (windows-2022) has been failing in the Normalize File and Directory Timestamps step with:

mtimehash: command not found
##[error]Process completed with exit code 127.

before any tests run, which trips the aggregate required gate.

Root cause: the Install Go mise tools step had no shell:, so on Windows it ran under PowerShell, while ./.github/scripts/retry.sh is a bash script (#!/usr/bin/env bash). The step silently no-oped on Windows (zero output), so mtimehash was only present when the mise tool cache was warm. On a cache miss it was never installed, and the normalize step failed with exit 127. main stays green only because the cache is usually warm — both green and failing runs use the same depot-windows-2022-16 runner, so this is not a fork/runner-routing issue.

Pre-existing CI-tooling issue, unrelated to the change that surfaced it (a Helm-only community PR, #27360).

Fix

One line: pin the step to shell: bash so the install actually runs on Windows and repairs a cache miss instead of being silently skipped.

Verification

$ bash ./.github/scripts/retry.sh --max-attempts 1 -- echo "retry.sh OK under bash"
retry.sh OK under bash

$ GOBIN=/tmp/demobin go install github.com/slsyy/mtimehash/cmd/[email protected]
$ ls -l /tmp/demobin/mtimehash
-rwxr-xr-x 1 coder coder 6692858 /tmp/demobin/mtimehash

# the tool that was "command not found" now runs and rewrites the mtime:
$ printf 'hello' > /tmp/mt.txt                 # mtime 2026-07-24 15:32
$ find /tmp/mt.txt | /tmp/demobin/mtimehash    # exit 0
$ # mtime now 1997-11-30 (content-hash derived)

Final confirmation is this PR's own test-go-pg (windows-2022) run. Note: if the mise cache is warm on this run the job passes regardless; the fix specifically hardens the cache-miss path this step exercises on Windows.

Follow-up (not in this PR)

• Make the normalize step resilient (skip when mtimehash is absent / invoke via mise exec) so a missing cache optimizer can't hard-fail the job.
• Audit other Windows run: steps that invoke retry.sh/bash scripts without shell: bash.

Linear: DOCS-605

This PR was created with AI assistance (Coder Agents).