l10n: de.po: Fix typo in German translation

Fix translation error of "complete => "vollständig" instead of
"unvollständig"

Currently: Documentation states that --unshallow can NOT be used on
INcomplete projects. This is wrong;
Correct would be: --unshallow can NOT be used on complete projects.

This change fixes that error in the German translation.

Signed-off-by: Philipp Weißmann <[email protected]>
Reviewed-by: Matthias Rüster <[email protected]>

Author: derphilipp

po/de.po

@@ -12796,7 +12796,7 @@ msgstr ""
 #: builtin/fetch.c:1603
 msgid "--unshallow on a complete repository does not make sense"
 msgstr ""
-"Die Option --unshallow kann nicht in einem Repository mit unvollständiger "
+"Die Option --unshallow kann nicht in einem Repository mit vollständiger "
 "Historie verwendet werden."
 
 #: builtin/fetch.c:1619