Running parallel builds from jenkins pipeline job triggers and waits for same job on other project
Something needs to be different in other_job2 for tests['x'] and tests['y'].

Example(untested),

for (f in [ 'x', 'y' ]) { {
    {some code}
    build job: "other_job2", parameters: [file_params, string(name:'dummy', value: "${f}")], wait: true, propagate: true
    // the dummy parameter is for preventing mutation
}


More info:
https://www.jenkins.io/doc/pipeline/examples/#jobs-in-parallel