test(ext/sw): assert PUT method on GitHub writeFileCreateOnly create path

Mirrors the POST assertion already present in the Gitea "creates" test —
catches accidental method drift.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

extension/src/service-worker/__tests__/git-host-extensions.test.ts

@@ -107,5 +107,6 @@ describe('writeFileCreateOnly (GitHub)', () => {
     const host = new GitHubHost('user/vault', 'tok');
     await host.writeFileCreateOnly('manifest.enc', new Uint8Array([1]), 'init');
     expect(fetchSpy).toHaveBeenCalledTimes(2);
+    expect((fetchSpy.mock.calls[1][1] as RequestInit).method).toBe('PUT');
   });
 });