selftests/powerpc/pmu/: Add check_extended_reg_test to .gitignore

Add the check_extended_reg_test binary to .gitignore to avoid accidentally
staging the build artifact.

Signed-off-by: Gopi Krishna Menon <krishnagopi487@gmail.com>
Tested-by: Aditya Bodkhe <adityab1@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250922004439.2395-1-krishnagopi487@gmail.com

Author: gopi487krishna

tools/testing/selftests/powerpc/pmu/sampling_tests/.gitignore

@@ -1,5 +1,6 @@
 bhrb_filter_map_test
 bhrb_no_crash_wo_pmu_test
+check_extended_reg_test
 intr_regs_no_crash_wo_pmu_test
 mmcr0_cc56run_test
 mmcr0_exceptionbits_test