Auto merge of #22673 - shanavas786:fix-servo-is-alive, r=jdm

Fix ServoDriver is_alive method

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #22664

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because it fixes test runner

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tests/wpt/metadata/MANIFEST.json

@@ -675404,7 +675404,7 @@
    "support"
   ],
   "tools/wptrunner/wptrunner/browsers/servodriver.py": [
-   "0a63a32c96699a441ce696bae6b8d32f4d69bc3d",
+   "75cee5abb68a67ebf624be28294a635ce5790cba",
    "support"
   ],
   "tools/wptrunner/wptrunner/browsers/webkit.py": [

tests/wpt/web-platform-tests/tools/wptrunner/wptrunner/browsers/servodriver.py

@@ -166,9 +166,7 @@ class ServoWebDriverBrowser(Browser):
                                    command=" ".join(self.command))
 
     def is_alive(self):
-        if self.runner:
-            return self.runner.is_running()
-        return False
+        return self.proc.poll() is None
 
     def cleanup(self):
         self.stop()