t3416: preemptively adjust alignment in a comment

We are about to adjust t3416 for the new default branch name `main`.
This name is two characters shorter and therefore needs two spaces more
padding to align correctly.

Adjusting the alignment before the big search-and-replace makes it
easier to verify that the final result does not leave any misaligned
lines behind.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3416-rebase-onto-threedots.sh

@@ -15,7 +15,7 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 #
 #	    F---G topic                             G'
 #	   /                                       /
-# A---B---C---D---E master      -->       A---B---C---D---E
+# A---B---C---D---E master        -->       A---B---C---D---E
 #      \   \ /
 #	\   x
 #	 \ / \