dtrace tests: Fix finding multiple process results

[bdrewery]

Summary

When looking up self process we can use ps -p $$ directly rather
than grep which may find other processes ending in the expected PID.

Sponsored by: Dell Inc.

Test Plan

/usr/tests/cddl/usr.sbin/dtrace/common/scripting # kyua test
t_dtrace_contrib:err_D_MACRO_UNDEF_invalidargs_d  ->  passed  [0.366s]
t_dtrace_contrib:err_D_OP_LVAL_rdonly_d  ->  passed  [0.370s]
t_dtrace_contrib:err_D_OP_WRITE_usepidmacro_d  ->  passed  [0.372s]
t_dtrace_contrib:err_D_SYNTAX_concat_d  ->  passed  [0.313s]
t_dtrace_contrib:err_D_SYNTAX_desc_d  ->  passed  [0.382s]
t_dtrace_contrib:err_D_SYNTAX_inval_d  ->  passed  [0.386s]
t_dtrace_contrib:err_D_SYNTAX_pid_d  ->  passed  [0.402s]
t_dtrace_contrib:tst_D_MACRO_UNUSED_overflow_ksh  ->  passed  [0.368s]
t_dtrace_contrib:tst_arg0_d  ->  passed  [0.651s]
t_dtrace_contrib:tst_arguments_ksh  ->  passed  [0.539s]
t_dtrace_contrib:tst_assign_d  ->  passed  [0.547s]
t_dtrace_contrib:tst_basic_d  ->  passed  [0.587s]
t_dtrace_contrib:tst_egid_d  ->  passed  [0.613s]
t_dtrace_contrib:tst_egid_ksh  ->  passed  [0.552s]
t_dtrace_contrib:tst_euid_d  ->  passed  [0.527s]
t_dtrace_contrib:tst_euid_ksh  ->  passed  [0.476s]
t_dtrace_contrib:tst_gid_d  ->  passed  [0.600s]
t_dtrace_contrib:tst_gid_ksh  ->  passed  [0.547s]
t_dtrace_contrib:tst_pgid_d  ->  passed  [0.667s]
t_dtrace_contrib:tst_pid_d  ->  passed  [0.597s]
t_dtrace_contrib:tst_ppid_d  ->  passed  [0.599s]
t_dtrace_contrib:tst_ppid_ksh  ->  passed  [0.577s]
t_dtrace_contrib:tst_projid_d  ->  passed  [0.600s]
t_dtrace_contrib:tst_projid_ksh  ->  expected_failure: test is known to fail: atf-check failed; see the output of the test for details  [0.335s]
t_dtrace_contrib:tst_quite_d  ->  passed  [0.570s]
t_dtrace_contrib:tst_sid_d  ->  passed  [0.535s]
t_dtrace_contrib:tst_sid_ksh  ->  passed  [0.538s]
t_dtrace_contrib:tst_stringmacro_ksh  ->  passed  [0.521s]
t_dtrace_contrib:tst_taskid_d  ->  passed  [0.551s]
t_dtrace_contrib:tst_taskid_ksh  ->  expected_failure: test is known to fail: atf-check failed; see the output of the test for details  [0.340s]
t_dtrace_contrib:tst_trace_d  ->  passed  [0.611s]
t_dtrace_contrib:tst_uid_d  ->  passed  [0.598s]
t_dtrace_contrib:tst_uid_ksh  ->  passed  [0.496s]

Results file id is usr_tests_cddl_usr.sbin_dtrace_common_scripting.20260703-005239-360845
Results saved to /root/.kyua/store/results.usr_tests_cddl_usr.sbin_dtrace_common_scripting.20260703-005239-360845.db

33/33 passed (0 broken, 0 failed, 0 skipped)