Fix typo in invoke_parallel.

This resulted from an merge gone wrong.
4 jobs from master in 3 minutes 44 seconds (queued for 9 seconds)
Status Job ID Name Coverage
  Build
passed #2916
build_cmake

00:44

 
  Test
passed #2917
run_tests

00:42

 
  Sanitizer
passed #2919
run_address_sanitizer

01:20

passed #2918
run_thread_sanitizer

00:56