testsuite: Update test for PR115537 to use SVE .

The PR was about SVE codegen, the testcase accidentally used neoverse-n1
instead of neoverse-v1 as was the original report.

This updates the tool options.

gcc/testsuite/ChangeLog:

	PR tree-optimization/115537
	* gcc.dg/vect/pr115537.c: Update flag from neoverse-n1 to neoverse-v1.