CI: make sure Paparazzi test failures stop the test flow (#117)

* Run Paparazzi tests just once when koverMergedReport is used.
* Make sure a Paparazzi failure breaks the test flow and blocks merging.
* Change ./gradlew check call in quality.yml to custom runQualityChecks task.

tests/uitests/src/test/kotlin/io/element/android/tests/uitests/ScreenshotTest.kt

@@ -67,7 +67,7 @@ class ScreenshotTest {
 
     @get:Rule
     val paparazzi = Paparazzi(
-        maxPercentDifference = 0.0,
+        maxPercentDifference = 0.01,
     )
 
     @Test