tests: explicitly request changed version in c/d conflict in test-commit-amend.t

We're going to change the default for this in an upcoming patch, but in this
instance we do want to continue picking the changed version.

tests/test-commit-amend.t

@@ -810,7 +810,9 b' Amend a merge changeset (with manifest-l'
   $ hg up -q default
   $ echo aa >> aa
   $ hg ci -m aa
-  $ hg merge -q bar
+  $ hg merge -q bar --config ui.interactive=True << EOF
+  > c
+  > EOF
   local changed aa which remote deleted
   use (c)hanged version, (d)elete, or leave (u)nresolved? c
   $ hg ci -m 'merge bar (with conflicts)'