ci(desktop-release): run the dependency install step under bash on Windows - #12423

What this PR does

Declares shell: 'bash' on the Install Qwen Code dependencies step of the desktop release workflow, so the Windows build runs that step's bash conditional under Git Bash instead of handing it to pwsh. Three lines, no other change.

Why it's needed

The step body became bash in #11859 (the pnpm switch). This workflow has no defaults.run block — unlike ci.yml, which is exactly why the same snippet is safe there — and each of its other nine bash-bodied steps declares shell: 'bash' individually. This one arrived without it, so on windows-latest the runner wrote the body to a .ps1 file and pwsh rejected line 2 with Missing '(' after 'if' in if statement. The job died in 56 s at step 11 of 38, every later step was skipped, and v0.24.2 published no Windows artifact while macOS arm64, macOS x64 and Linux x64 all succeeded.

Nothing has touched the file since, so the daily packaging check has been red on Windows two days running (09-20 and 09-21), and v0.24.3 was cut today — the next desktop release fails the same way.

Reviewer Test Plan

How to verify

1. Read the failing log: run 35616657702 → Build Windows x64. It shows shell: C:\Program Files\PowerShell\7\pwsh.EXE -command ". '{0}'", then ParserError: ...ps1:2, then exit code 1 at step 11.
2. In that same job on that same runner, eight earlier steps completed successfully under C:\Program Files\Git\bin\bash.EXE --noprofile --norc -e -o pipefail {0} — precisely the ones that declare shell: 'bash'. Git Bash is present, so the declaration is the only thing missing.
3. After merge: re-dispatch desktop-packaging-check.yml (or wait for the 16:00 UTC daily) and confirm Build Windows x64 gets past step 11 and reaches Smoke packaged application.

Evidence (Before & After)

Before, verbatim from the run above:

##[group]Run if [ -f pnpm-lock.yaml ]; then
shell: C:\Program Files\PowerShell\7\pwsh.EXE -command ". '{0}'"
ParserError: D:\a\_temp\33b4c2f7-5b4f-4e61-a80a-971e51d35e67.ps1:2
   2 |  if [ -f pnpm-lock.yaml ]; then
     |    ~
     | Missing '(' after 'if' in if statement.
##[error]Process completed with exit code 1.

After: not observable from a PR, because this workflow runs on workflow_dispatch, on release, and on the daily schedule — not on pull_request. What was checked locally: the file still parses as YAML and has exactly one Install Qwen Code dependencies step, now carrying shell: bash with its bash body intact; prettier reports no formatting change; .yamllint.yml defines no line-length rule for the added comment.

Tested on

Environment (optional)

N/A.

Risk & Scope

• Main risk or tradeoff: essentially none. shell: 'bash' on Windows resolves to the Git Bash that eight sibling steps in the same job already use successfully, the step body is untouched, and Linux/macOS behaviour is identical because bash is already their default.
• Not validated / out of scope: this does not prove the rest of the Windows packaging path works. It has not run past step 11 since 09-20, so steps 12–38 (bundled runtime, tauri build, NSIS installer, packaged smoke) are unexercised and could surface a second, separate failure. The next packaging check will say.
• Breaking changes / migration notes: none.

Linked Issues

Fixes #12414

##[group]Run if [ -f pnpm-lock.yaml ]; then
shell: C:\Program Files\PowerShell\7\pwsh.EXE -command ". '{0}'"
ParserError: D:\a\_temp\33b4c2f7-5b4f-4e61-a80a-971e51d35e67.ps1:2
   2 |  if [ -f pnpm-lock.yaml ]; then
     |    ~
     | Missing '(' after 'if' in if statement.
##[error]Process completed with exit code 1.