Update pennylane requirement from ~=0.30.0 to ~=0.31.0 (#1888)

* Update pennylane requirement from ~=0.30.0 to ~=0.31.0

Updates the requirements on [pennylane](https://github.com/PennyLaneAI/pennylane) to permit the latest version.
- [Release notes](https://github.com/PennyLaneAI/pennylane/releases)
- [Commits](PennyLaneAI/pennylane@v0.30.0...v0.31.0)

---
updated-dependencies:
- dependency-name: pennylane
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

* `pennylane.grouping` moved/organized to `pennylane.pauli`

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: nate stemen <nate@unitary.fund>

dev_requirements.txt

@@ -4,7 +4,7 @@ qiskit-aer~=0.12.2
 qiskit-ibm-provider~=0.6.2
 pyquil~=3.5.4
 pennylane-qiskit~=0.31.0
-pennylane~=0.30.0
+pennylane~=0.31.0
 amazon-braket-sdk~=1.52.0
 
 # Unit tests, coverage, and formatting/style.

docs/source/examples/molecular_hydrogen_pennylane.md

@@ -1,7 +1,7 @@
 ---
 jupytext:
   text_representation:
-    extension: .myst
+    extension: .md
     format_name: myst
     format_version: 0.13
     jupytext_version: 1.11.1
@@ -37,7 +37,7 @@ from scipy.optimize import brute
 import cirq
 
 import pennylane as qml
-from pennylane.grouping import pauli_word_to_string
+from pennylane.pauli import pauli_word_to_string
 
 import mitiq
 from mitiq import zne  # Zero-noise extrapolation module