Fix unit tests after changing branches too eagerly

Commit 108fb918 was a bit too eager in changing the branch names and also
changed the ones in the unit tests, breaking them since the reference files
weren't update accordingly.

Revert those changes so that unit tests pass again.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

atc_renderer/tests_files/test_file1.yaml

@@ -59,7 +59,7 @@ metadata:
 install:
   git-repos:
     - url: https://gitlab.apertis.org/infrastructure/apertis-tests.git
-      branch: 'apertis/v2019dev0'
+      branch: master
 
 run:
   steps:

atc_renderer/tests_files/test_file4.yaml

@@ -36,7 +36,7 @@ metadata:
 install:
   git-repos:
     - url: https://gitlab.apertis.org/tests/apparmor.git
-      branch: 'apertis/v2019dev0'
+      branch: master
 
 run:
   steps:

atc_renderer/tests_files/test_file5.yaml

@@ -37,7 +37,7 @@ install:
     - chown user:user -R /tmp/ribchester-*
   git-repos:
     - url: https://gitlab.apertis.org/infrastructure/apertis-tests.git
-      branch: 'apertis/v2019dev0'
+      branch: master
 
 run:
   steps: