fix the test script so it works outside flatpak again

scripts/test.sh

@@ -2,14 +2,17 @@
 
 set -o errexit
 set -o pipefail
+set -x
 
+# $1 Passed by meson and should be the builddir
 export CARGO_TARGET_DIR="$1/target/"
 
 # If this is run inside a flatpak envrironment, append the export the rustc
 # sdk-extension binaries to the path
-if [ -n "/.flatpak-info" ]
+if [ -f "/.flatpak-info" ]
 then
     export PATH="$PATH:/usr/lib/sdk/rust-stable/bin"
+    # This assumes its run inside a Builder terminal
     export CARGO_TARGET_DIR="$BUILDDIR/target/"
 fi