build(deps): bump robolectric from 4.7.3 to 4.8

Bumps [robolectric](https://github.com/robolectric/robolectric) from 4.7.3 to 4.8.
- [Release notes](https://github.com/robolectric/robolectric/releases)
- [Commits](robolectric/robolectric@robolectric-4.7.3...robolectric-4.8)

---
updated-dependencies:
- dependency-name: org.robolectric:robolectric
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

build.gradle

@@ -42,7 +42,7 @@ buildscript {
         androidXTestCoreVersion = '1.4.0'
         androidXTestExtKotlinRunnerVersion = '1.1.3'
         androidXTestRulesVersion = '1.2.0-beta01'
-        robolectricVersion = '4.7.3'
+        robolectricVersion = '4.8'
         archTestingVersion = '2.1.0'
         espressoVersion = '3.4.0'