Skip compositor tests without recording a failure

Two problems made a missing Wayland compositor look like broken tests.

The cleanup traps ended on a bare conditional, so when a test skipped
before creating its TMPDIR the trap's last command returned 1 and, under
set -e, that overrode the explicit exit 0.

Six tests that launch quickshell had no compositor guard at all, so they
ran anyway and failed on the Qt platform plugin.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

test/shell.d/toggle-test.sh

@@ -9,7 +9,9 @@ TMPDIR=""
 export PATH="$ROOT/bin:$PATH"
 
 cleanup() {
-  [[ -n $TMPDIR && -d $TMPDIR ]] && rm -rf "$TMPDIR"
+  if [[ -n $TMPDIR && -d $TMPDIR ]]; then
+    rm -rf "$TMPDIR"
+  fi
 }
 trap cleanup EXIT