Error out if run-full-tests is run not inside a test container.

scripts/run-full-tests

@@ -8,7 +8,14 @@
 # For more information, see:
 # https://torsion.org/borgmatic/docs/how-to/develop-on-borgmatic/
 
-set -ex
+set -e
+
+if [ -z "$TEST_CONTAINER" ] ; then
+    echo "This script is designed to work inside a test container and is not intended to"
+    echo "be run manually. If you're trying to run borgmatic's end-to-end tests, execute"
+    echo "scripts/run-end-to-end-dev-tests instead."
+    exit 1
+fi
 
 apk add --no-cache python3 py3-pip borgbackup postgresql-client mariadb-client mongodb-tools \
     py3-ruamel.yaml py3-ruamel.yaml.clib bash sqlite