fix: use full path to pactflow binary as it may be invoked from anywh… #31

Job	Run time
build-and-test (16.x, windows-2019)	3m 33s
build-and-test (16.x, macos-latest)	4m 30s
build-and-test (16.x, ubuntu-latest)	2m 46s
build-and-test (18.x, windows-2019)	5m 21s
build-and-test (18.x, macos-latest)	1m 25s
build-and-test (18.x, ubuntu-latest)	2m 3s
build-and-test (20.x, windows-2019)	3m 20s
build-and-test (20.x, macos-latest)	2m 10s
build-and-test (20.x, ubuntu-latest)	1m 13s
	26m 21s

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