'make test': Fix breakage introduced by 4d3da30f8b:

test failure would not be reflected by the exit code of 'make'.

Setting a shell parameter in the left-hand side of a pipe is not visible to
commands after the pipe, because the left-hand side forks.  (That's true both
in 'sh' used by 'make' and in 'zsh' that runs tests/test-highlighting.zsh, at
least on my system.)  Therefore, move the colorizing hook to where it doesn't
interfere with setting the $something_failed (in tests/test-highlighting.zsh)
and $result (in Makefile) parameters.

Makefile

@@ -26,7 +26,7 @@ test:
 			$(ZSH) -f tests/test-highlighting.zsh "$${test##*/}"; \
 			: $$(( result |= $$? )); \
 		fi \
-	done | $(ZSH) -f tests/tap-colorizer.zsh; \
+	done; \
 	exit $$result
 
 perf: