Widen mancheck to all of man and test-runner

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12125

Makefile.am

@@ -170,7 +170,7 @@ checkbashisms:
 PHONY += mancheck
 mancheck:
 	@if type mandoc > /dev/null 2>&1; then \
-		find ${top_srcdir}/man/man8 -type f -name '*[1-9]*' \
+		find ${top_srcdir}/man ${top_srcdir}/tests/test-runner/man -type f -name '*[1-9]*' \
 			-exec mandoc -Tlint -Werror {} \+; \
 	else \
 		echo "skipping mancheck because mandoc is not installed"; \