test: disable flaky transparent window test (#35708)

Co-authored-by: Jeremy Rose <[email protected]>

spec-main/api-browser-window-spec.ts

@@ -2068,7 +2068,8 @@ describe('BrowserWindow module', () => {
       }).to.not.throw();
     });
 
-    it('Allows setting a transparent window via CSS', async () => {
+    // TODO(nornagon): disabled due to flakiness.
+    it.skip('Allows setting a transparent window via CSS', async () => {
       const appPath = path.join(__dirname, 'fixtures', 'apps', 'background-color-transparent');
 
       appProcess = childProcess.spawn(process.execPath, [appPath]);