[ Device Lab ] Fix wakefulness check to only match log entries with string values (flutter#174953)

Sometimes there can be multiple wakefulness log entries (e.g.,
'mWakefulness=Awake' and 'mWakefulness=1'), but we only care about the
entry with a string value.

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Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: 2 people

dev/devicelab/lib/framework/devices.dart

@@ -685,7 +685,7 @@ class AndroidDevice extends Device {
     final String powerInfo = await shellEval('dumpsys', <String>['power']);
     // A motoG4 phone returns `mWakefulness=Awake`.
     // A Samsung phone returns `getWakefullnessLocked()=Awake`.
-    final RegExp wakefulnessRegexp = RegExp(r'.*(mWakefulness=|getWakefulnessLocked\(\)=).*');
+    final RegExp wakefulnessRegexp = RegExp(r'(?:mWakefulness|getWakefulnessLocked\(\))=[a-zA-Z]+');
     final String wakefulness = grep(wakefulnessRegexp, from: powerInfo).single.split('=')[1].trim();
     return wakefulness;
   }