Analysis: Resolve unnecessary safe call type warning for ui tests

Warning Message: "Unnecessary safe call on a non-null receiver of type
kotlin.collections.ArrayList<IAztecPlugin> /* =
java.util.ArrayList<IAztecPlugin> */. This expression will have nullable
type in future releases"

app/src/androidTest/kotlin/org/wordpress/aztec/demo/tests/GutenbergCompatTests.kt

@@ -328,7 +328,7 @@ class GutenbergCompatTests : BaseTest() {
         val editorPage = EditorPage()
         val audioShortcodePlugin = AudioShortcodePlugin()
         val aztecText = mActivityIntentsTestRule.activity.findViewById<AztecText>(R.id.aztec)
-        aztecText.plugins?.add(audioShortcodePlugin)
+        aztecText.plugins.add(audioShortcodePlugin)
 
         // let's test the plugin works as expected, i.e. it preserves the Gutenberg block structure
         editorPage