Update how we check for graphviz installation

Author: mudit2812

frontend/test/pytest/python_interface/inspection/test_mlir_graph.py

@@ -14,7 +14,7 @@
 """Unit test module for the MLIR graph generation in the Unified Compiler visualization module."""
 
 from pathlib import Path
-from subprocess import run
+from shutil import which
 
 import pennylane as qml
 import pytest
@@ -28,7 +28,7 @@
 pytestmark = pytest.mark.xdsl
 graphviz = pytest.importorskip("graphviz")
 
-if run(["/usr/bin/which", "dot"], check=False).returncode != 0:
+if which("dot") is None:
     pytest.skip(reason="Graphviz isn't installed.")