tests: Fix cockpit-appstream detection

cwd in run-tests.sh is just the test user's home directory. Look into
the original test unpack directory for the cockpit-appstream spec file.

tests/run-test.sh

@@ -1,11 +1,13 @@
 #!/bin/sh
 set -eux
 
+cd "$SOURCE"
+
 . /etc/os-release
 test_optional=
 test_basic=
 
-if ls $(pwd)/cockpit-appstream* 1> /dev/null 2>&1; then
+if ls ../cockpit-appstream* 1> /dev/null 2>&1; then
     test_optional=1
 else
     test_basic=1
@@ -17,7 +19,6 @@ if [ "$ID" = "fedora" ]; then
 fi
 
 # tests need cockpit's bots/ libraries
-cd "$SOURCE"
 git clone --depth=1 https://github.com/cockpit-project/bots
 
 # only install a subset to save time/space