test_os permanently change the process priority

[serhiy-storchaka]

Bug report

ProgramPriorityTests in test_os changes the process priority (makes it less prioritized in the scheduler) and then tries to restore the old value, why is fail unless the test is ran as root. It affects all further tests if run in sequential mode and all further tests in test_os if run in parallel mode. It can makes the testing process less responsible and make some tests (especially relying on timeouts or interruption) unstable.

This test should be run in a separate subprocess.

Linked PRs

• gh-115596: Fix ProgramPriorityTests in test_os permanently changing the process priority #115610
• [3.12] gh-115596: Fix ProgramPriorityTests in test_os permanently changing the process priority (GH-115610) #115616
• [3.11] gh-115596: Fix ProgramPriorityTests in test_os permanently changing the process priority (GH-115610) #115617