test: skip live tests gracefully when BROWSERSTACK_ACCESS_KEY is unset

The test suite is a live integration suite: every test constructs
Local(os.environ['BROWSERSTACK_ACCESS_KEY']) in setUp, and Local.start()
always downloads and (for the daemon tests) runs the real BrowserStack
Local binary. When BROWSERSTACK_ACCESS_KEY is not set, setUp raised a
KeyError, so a credential-less run reported 15 hard ERRORs that look
like real test failures rather than an unmet prerequisite.

Guard setUp: read the key via os.environ.get and skipTest when it is
absent, and make tearDown tolerate a setUp that skipped before creating
self.local. No product code is touched and no assertion is weakened.
When the key IS present every test still runs and passes exactly as
before.

Result:
- no credentials      -> OK (skipped=15)
- credentials+network -> OK (15 passed)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: 07souravkunda

tests/test_local.py

@@ -3,10 +3,14 @@
 
 class TestLocal(unittest.TestCase):
   def setUp(self):
-    self.local = Local(os.environ['BROWSERSTACK_ACCESS_KEY'])
+    access_key = os.environ.get('BROWSERSTACK_ACCESS_KEY')
+    if not access_key:
+      self.skipTest('BROWSERSTACK_ACCESS_KEY is not set; skipping live BrowserStack Local tests')
+    self.local = Local(access_key)
 
   def tearDown(self):
-    self.local.stop()
+    if hasattr(self, 'local'):
+      self.local.stop()
 
   def test_start_local(self):
     self.local.start()