Recognizing Launcher builds consisting only of digits

Bug: 206687633
Test: online regex tools
Change-Id: Ia6155f22fb9a0eba3beb6edb607f44f901629330

tests/src/com/android/launcher3/util/rule/TestStabilityRule.java

@@ -41,7 +41,7 @@ public class TestStabilityRule implements TestRule {
             Pattern.compile("^("
                     + "(?<local>(BuildFromAndroidStudio|"
                     + "([0-9]+|[A-Z])-eng\\.[a-z]+\\.[0-9]+\\.[0-9]+))|"
-                    + "(?<platform>[A-Z]([a-z]|[0-9])*)"
+                    + "(?<platform>([A-Z][a-z]*[0-9]*|[0-9]+)*)"
                     + ")$");
     private static final Pattern PLATFORM_BUILD =
             Pattern.compile("^("