twister: reporting: fix gcov_tool path on Windows #158077

Job	Run time
twister-build-prep / prep_pr	3m 52s
twister-build-prep / prep_push	0s
twister-build (1)	36m 1s
twister-build (2)	32m 47s
twister-build (3)	35m 47s
twister-build (4)	35m 34s
twister-build (5)	22m 19s
twister-build (6)	27m 38s
twister-build (7)	27m 10s
Publish Unit Tests Results	11s
Check Twister Status / all jobs passed	1s
	3h 41m 20s

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