Update testharness to read version from libs.versions.toml

Changes testharness module to read versionCode and versionName from
libs.versions.toml instead of using hardcoded values. This aligns
with the pattern used by app and authenticator modules and ensures
the setBuildVersionInfo Fastlane task in the workflow actually
updates the testharness build version.

Before:
  versionCode = 1
  versionName = "1.0.0"

After:
  versionCode = libs.versions.appVersionCode.get().toInt()
  versionName = libs.versions.appVersionName.get()

Addresses Finding 3 from code review of PR #6181.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: SaintPatrck

testharness/build.gradle.kts

@@ -19,8 +19,8 @@ android {
         // API 28 - CredentialManager with Play Services support
         minSdk = libs.versions.minSdkBwa.get().toInt()
         targetSdk = libs.versions.targetSdk.get().toInt()
-        versionCode = 1
-        versionName = "1.0.0"
+        versionCode = libs.versions.appVersionCode.get().toInt()
+        versionName = libs.versions.appVersionName.get()
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }