patch 8.2.0527: Vim9: function types insufficiently tested

Problem:    Vim9: function types insufficiently tested.
Solution:   Add more tests.  Fix white space check.  Add "test_vim9" target.
diff --git a/src/Makefile b/src/Makefile
index 704721b..c32ea08 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -2301,7 +2301,7 @@
 #	export TEST_FILTER=Test_terminal_wipe_buffer
 # A partial match also works:
 #	export TEST_FILTER=wipe_buffer
-$(NEW_TESTS):
+$(NEW_TESTS) test_vim9:
 	cd testdir; $(MAKE) $@ VIMPROG=../$(VIMTESTTARGET) $(GUI_TESTARG) SCRIPTSOURCE=../$(SCRIPTSOURCE)
 
 newtests: