build: ensure test is running on git commit that this code works with

Since https://gitlab.com/fdroid/ci-test-app is a separate git repo, things
with incompatible changes could get out of sync.  Therefore, this test
should specify which git commit is runs against.

For example, the .fdroid.yml file is still a moving target.  Just now, the
keys had the spaces removed as part of this MR.

tests/run-tests

@@ -144,6 +144,10 @@ $fdroid update
 echo_header 'run `fdroid build` in fresh git checkout from import.TestCase'
 
 cd $WORKSPACE/tests/tmp/importer
+git remote update -p
+git clean -fdx
+# stick with known working commit, in case future commits break things for this code
+git reset --hard cecf00c08aec56ae7a5eba444150c4d1ae868814
 if [ -d $ANDROID_HOME/platforms/android-23 ]; then
     echo "build_tools = '`ls -1 $ANDROID_HOME/build-tools/ | sort -n | tail -1`'" > config.py
     echo "force_build_tools = True" >> config.py