Merge pull request matplotlib#27581 from tacaswell/ci/de_locale

CI: install German lanugage packs an ubuntu test runners

Author: dstansby

.github/workflows/tests.yml

@@ -119,6 +119,7 @@ jobs:
               gir1.2-gtk-3.0 \
               graphviz \
               inkscape \
+              language-pack-de \
               lcov \
               libcairo2 \
               libcairo2-dev \

azure-pipelines.yml

@@ -103,6 +103,7 @@ stages:
               gir1.2-gtk-3.0 \
               graphviz \
               inkscape \
+              language-pack-de \
               lcov \
               libcairo2 \
               libgirepository-1.0-1 \