test(e2e, android): use api21 emulator

If we say we support minSdkVersion 16 we should get as close as possible
to actually supporting it. 16 is sometimes problematic as an emulator and
requires multidex (already removed from our tests app...) but 21 is still
interesting since it is below 24 (Java 8 support on device), is minSdkVersion
for react-native 0.64 (current)  and it was a reliable emulator previously

.github/workflows/tests_e2e.yml

@@ -128,7 +128,7 @@ jobs:
           command: echo "y" | $ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager --install "system-images;android-30;google_apis;x86_64"
 
       - name: Create Emulator
-        run: echo "no" | $ANDROID_HOME/cmdline-tools/latest/bin/avdmanager create avd --force --name TestingAVD --device "Nexus 5X" -k 'system-images;android-30;google_apis;x86_64' -g google_apis
+        run: echo "no" | $ANDROID_HOME/cmdline-tools/latest/bin/avdmanager create avd --force --name TestingAVD --device "Nexus 5X" -k 'system-images;android-21;google_apis;x86_64' -g google_apis
 
       # These Emulator start steps are the current best practice to do retries on multi-line commands with persistent (nohup) processes
       - name: Start Android Emulator