[pigeon]: Bump mockk (#3109)

Bumps [mockk](https://github.com/mockk/mockk) from 1.13.3 to 1.13.4.
- [Release notes](https://github.com/mockk/mockk/releases)
- [Commits](https://github.com/mockk/mockk/compare/1.13.3...v1.13.4)

---
updated-dependencies:
- dependency-name: io.mockk:mockk
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

packages/pigeon/platform_tests/test_plugin/android/build.gradle

@@ -58,6 +58,6 @@ android {
 
     dependencies {
         testImplementation 'junit:junit:4.+'
-        testImplementation "io.mockk:mockk:1.13.3"
+        testImplementation "io.mockk:mockk:1.13.4"
     }
 }