Rename test_simplify_with_adjoint_not_defined in test_pow_ops.py

[willjmax]

This PR renames test_simplify_with_adjoint_not_defined to test_simplify_with_pow_not_defined in the test_pow_ops.py file. The test is given by the following code.

    def test_simplify_with_adjoint_not_defined(self):
        """Test the simplify method with an operator that has not defined the op.pow method."""
        op = Pow(qml.U2(1, 1, 0), z=3)
        simplified_op = op.simplify()
        assert isinstance(simplified_op, Pow)
        assert op.data == simplified_op.data
        assert op.wires == simplified_op.wires
        assert op.arithmetic_depth == simplified_op.arithmetic_depth

Note the function name says adjoint is not defined, but the docstring says that pow is not defined. The docstring is correct, since qml.U2 defines the adjoint method.

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

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[albi3ro]

Don't think this needs a changelog entry, but I'm fine leaving it in anyway.

Thanks for catching this.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.39%. Comparing base (38a5140) to head (204d06a).
Report is 321 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6388   +/-   ##
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  Coverage   99.39%   99.39%           
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  Files         448      448           
  Lines       42464    42466    +2     
=======================================
+ Hits        42209    42211    +2     
  Misses        255      255           

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