Added SignUp Button Unit Test

[madhurgupta10]

Description
Added SignUp Button Unit Test.

Fixes #2686 Write Unit Test for Login Activity

Tests performed
Tested betaDebug on Xiaomi Mi A1 with API level 28 stock android.

Test Result

Testing started at 03:20 AM ...
03/21 03:20:42: Launching isSignUpButtonWorks()
$ adb push C:\Users\madhu\Desktop\apps-android-commons\app\build\outputs\apk\beta\debug\app-commons-v2.10.1-unit-test-login-beta-debug.apk /data/local/tmp/fr.free.nrw.commons.beta
$ adb shell pm install -t -r "/data/local/tmp/fr.free.nrw.commons.beta"
Success
APK installed in 2 s 252 ms
$ adb push C:\Users\madhu\Desktop\apps-android-commons\app\build\outputs\apk\androidTest\beta\debug\app-commons-v2.10.1-unit-test-login-beta-debug-androidTest.apk /data/local/tmp/fr.free.nrw.commons.beta.test
$ adb shell pm install -t -r "/data/local/tmp/fr.free.nrw.commons.beta.test"
Success
APK installed in 1 s 801 ms
Running tests
$ adb shell am instrument -w -r -e debug false -e class 'fr.free.nrw.commons.LoginActivityTest#isSignUpButtonWorks' fr.free.nrw.commons.beta.test/androidx.test.runner.AndroidJUnitRunner
Connected to process 29063 on device xiaomi-mi_a1-7af99b9c0404
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
I/rw.commons.bet: The ClassLoaderContext is a special shared library.
Started running tests
Tests ran to completion.

Test Passed

[codecov-io]

Codecov Report

Merging #2687 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #2687   +/-   ##
======================================
  Coverage    2.81%   2.81%           
======================================
  Files         258     258           
  Lines       12376   12376           
  Branches     1111    1111           
======================================
  Hits          349     349           
  Misses      12001   12001           
  Partials       26      26

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[domdomegg]

Nice. Ideally (can be fixed in another PR) more would be tested and it would check that the user was logged out before running these tests as currently they fail if the user is logged in (as the app redirects to MainActivity)

[madhurgupta10]

@domdomegg Sure, I will add more tests soon :)