[AIRFLOW-6839] even more mypy speed improvements (#7460)

Require_serial:true is better choice than pass_filename: false as it can
speed-up mypy for single file changes.

Significant gains can be achieved for single file changes and no cache for all
other files. This is majority of cases for our users who have pre-commits
installed as hooks because most people change only few files and never run
check with --all-files

When just one file is changed and no cache is built, the difference is drastic:

require_serial: true = 4s

pass_filenames: false =  13s