Use correct location for buck_to_junit (#27766)

Summary:
`test_android`'s Test Collection step fails when it attempts to convert buck's output to the junit-compatible format that Circle CI expects. Executing the script from the `okbuck` location should help here.

## Changelog

[Internal] - Use correct location for buck_to_junit in test_android CI step
Pull Request resolved: https://github.com/facebook/react-native/pull/27766

Test Plan: Circle CI

Differential Revision: D19403837

Pulled By: hramos

fbshipit-source-id: 44e599ab653e7412340c3dcfdc45c5d37bcea1ee

.circleci/config.yml

@@ -519,6 +519,7 @@ jobs:
             find . -type f -regex ".*/outputs/androidTest-results/connected/.*xml" -exec cp {} ./reports/outputs/ \;
             find . -type f -regex ".*/buck-out/gen/ReactAndroid/src/test/.*/.*xml" -exec cp {} ./reports/buck/ \;
             if [ -f ~/react-native/reports/buck/all-results-raw.xml ]; then
+              cd ~/okbuck
               ./tooling/junit/buck_to_junit.sh ~/react-native/reports/buck/all-results-raw.xml ~/react-native/reports/junit/results.xml
             fi
           when: always