Revert "Merge branch '63825-increase-rspec-parallelism' into 'master'"

This reverts merge request !30130

.gitlab/ci/rails.gitlab-ci.yml

@@ -139,7 +139,7 @@ setup-test-env:
 rspec unit pg:
   <<: *rspec-metadata-pg
-  parallel: 25
+  parallel: 20
 rspec integration pg:
   <<: *rspec-metadata-pg
@@ -152,7 +152,7 @@ rspec system pg:
 rspec unit pg-10:
   <<: *rspec-metadata-pg-10
   <<: *only-schedules-master
-  parallel: 25
+  parallel: 20
 rspec integration pg-10:
   <<: *rspec-metadata-pg-10