test(desktop): isolate Windows cache path from host platform

apps/desktop/tests/windows-sign.spec.ts

@@ -163,6 +163,7 @@ describe('Windows token signing', () => {
         DSH_DESKTOP_MANDATORY_UPDATE_TEST_ORIGIN: 'https://policy.example.com',
         DSH_DESKTOP_WINDOWS_CER_FILE: certificateFile, DSH_DESKTOP_WINDOWS_SIGNTOOL: signTool,
         DSH_DESKTOP_WINDOWS_TOKEN_PIN: 'fixture-pin', DSH_DESKTOP_WINDOWS_KEY_CONTAINER: 'fixture-container',
+        DSH_DESKTOP_WINDOWS_SIGNATURE_CACHE_DIR: 'C:\\fixture\\signature-cache',
       }, { platform: 'win32', arch: 'x64' })
       expect(execFile).not.toHaveBeenCalled()
       vi.mocked(execFile).mockImplementationOnce((...args: unknown[]) => {