ci: Increase tier 2 max-parallel

We have gained quite a few tier 2 jobs. Increase max-parallel so they don't take quite as long. (backport <#4776>) (cherry picked from commit e3cbac6)

Author: tgross35

.github/workflows/ci.yaml

@@ -159,7 +159,7 @@ jobs:
  needs: [test_tier1, style_check]
  strategy:
  fail-fast: true
- max-parallel: 12
+ max-parallel: 16
  matrix:
  include:
  # FIXME(sparc): this takes much longer to run than any other job, put