testsuite: plugin: Fix gcc.dg/plugin/crash-test-write-though-null-sarif.c on Solaris

gcc.dg/plugin/crash-test-write-though-null-sarif.c FAILs on Solaris:

FAIL: gcc.dg/plugin/crash-test-write-though-null-sarif.c -fplugin=./crash_test_plugin.so  scan-sarif-file "text": "Segmentation fault

Comparing the sarif files between Linux and Solaris reveals

-                                                            "message": {"text": "Segmentation fault"},
+                                                            "message": {"text": "Segmentation Fault"},

This patch allows for both forms.

Tested on i386-pc-solaris2.11, sparc-sun-solaris2.11, and
x86_64-pc-linux-gnu.

2024-02-22  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gcc/testsuite:
	* gcc.dg/plugin/crash-test-write-though-null-sarif.c
	(scan-sarif-file): Allow for "Segmentation Fault", too.