gitk: Update cherry-pick error message parsing

Commit 981ff5c37a changed the error
message from git cherry-pick from
    Automatic cherry-pick failed.  [...advice...]
to
    error: could not apply 7ab78c9... Do something neat.
    [...advice...]

Update gitk’s regex to match this, restoring the ability to launch git
citool to resolve conflicted cherry-picks.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -9065,7 +9065,7 @@ proc cherrypick {} {
 			to file '%s'.\nPlease commit, reset or stash\
 			your changes and try again." $fname]
 	} elseif {[regexp -line \
-		       {^(CONFLICT \(.*\):|Automatic cherry-pick failed)} \
+		       {^(CONFLICT \(.*\):|Automatic cherry-pick failed|error: could not apply)} \
 		       $err]} {
 	    if {[confirm_popup [mc "Cherry-pick failed because of merge\
 			conflict.\nDo you wish to run git citool to\