annotate-tests: override VISUAL when running tests.

The tests hang for me waiting for Emacs with its output directed
somewhere strage, because I hedged my bets and set both EDITOR and
VISUAL to run Emacs.

Signed-off-by: Mark Wooding <mdw@distorted.org.uk>
Signed-off-by: Junio C Hamano <junkio@cox.net>

t/annotate-tests.sh

@@ -94,7 +94,7 @@ test_expect_success \
 test_expect_success \
     'merge-setup part 4' \
     'echo "evil merge." >>file &&
-     EDITOR=: git commit -a --amend'
+     EDITOR=: VISUAL=: git commit -a --amend'
 
 test_expect_success \
     'Two lines blamed on A, one on B, two on B1, one on B2, one on A U Thor' \