fix: disable GPG signing in test fixtures

[altendky]

Issue for this PR

Closes #20385
Closes #18295

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds commit.gpgsign false to all test fixtures that create temporary git repositories. This prevents test failures when developers have GPG/SSH signing agents configured globally.

Previously, some tests used --no-gpg-sign flags on individual commit commands while others did not, causing inconsistent behavior. This fix centralizes the configuration in the fixtures so all commits in test repos inherit it automatically.

Changes:

• packages/opencode/test/fixture/fixture.ts - Added config to tmpdir() and tmpdirScoped()
• packages/opencode/test/project/migrate-global.test.ts - Added config (manually inits git)
• packages/app/e2e/actions.ts - Added config to createTestProject()
• Removed redundant --no-gpg-sign flags from test files that now inherit the setting

How did you verify your code works?

Ran all git-related unit tests with 1Password SSH agent configured: 145 pass, 13 skip, 0 fail.

Screenshots / recordings

N/A

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Related PR Found

PR #18296: chore(app): QOL: don't sign commits during e2e tests
#18296

Why it's related: This PR addresses the same underlying issue - disabling GPG/commit signing in tests. It appears to be a prior partial fix that focused on e2e tests. The current PR (20386) is a comprehensive follow-up that centralizes the configuration across all test fixtures and closes issue #18295 (likely related to PR 18296).