MFC r350211, r350220, r350235, r350238-r350239, r350295, r350512, r350700, r352219

r350211:
Temporarily skip flakey test case
sys.kern.ptrace_test.ptrace__follow_fork_child_detached_unrelated_debugger

PR: 239292
Sponsored by: The FreeBSD Foundation

r350220:
Fix URL.

Sponsored by: The FreeBSD Foundation

r350235:
Temporarily skip flakey test case
sys.kern.ptrace_test.ptrace__PT_KILL_competing_stop

PR: 220841
Sponsored by: The FreeBSD Foundation

r350238:
Temporarily skip flakey test case
sys.kern.ptrace_test.ptrace__follow_fork_both_attached_unrelated_debugger

PR: 239397
Sponsored by: The FreeBSD Foundation

r350239:
Temporarily skip flakey test case
sys.kern.ptrace_test.ptrace__parent_sees_exit_after_child_debugger

PR: 239399
Sponsored by: The FreeBSD Foundation

r350295:
Temporarily skip flakey test case
sys.kern.ptrace_test.ptrace__follow_fork_parent_detached_unrelated_debugger

PR: 239425
Sponsored by: The FreeBSD Foundation

r350512:
Only skip test cases sometimes failing in CI when they are running in CI

Suggested by: jhb
Sponsored by: The FreeBSD Foundation

r350700:
Get configuration variable with default value for not breaking default setting

Reported by: markj
Sponsored by: The FreeBSD Foundation

r352219:
Temporarily skip flakey test case sys.kern.ptrace_test.ptrace__getppid

PR: 240510
Sponsored by: The FreeBSD Foundation