Fix equality typos in Documentation for Ryy, Rxx and Rzx gates (backport #13226)

[mergify]

Summary

This PR resolves #13225 by fixing the typos in the documentation for the Ryy, Rxx and Rzx gates.

Details and comments

If I am not mistaken, these are the proper equalities. I also checked the result with numpy:

>>> import qiskit
>>> import numpy as np
>>> Ryy = qiskit.circuit.library.standard_gates.RYYGate(theta=np.pi)
>>> np.isclose(np.array(Ryy), -1j*np.kron(np.array(Y), np.array(Y)))
array([[ True,  True,  True,  True],
       [ True,  True,  True,  True],
       [ True,  True,  True,  True],
       [ True,  True,  True,  True]])
>>> Rxx = qiskit.circuit.library.standard_gates.RXXGate(theta=np.pi)
>>> np.isclose(np.array(Rxx), -1j*np.kron(np.array(X), np.array(X)))
array([[ True,  True,  True,  True],
       [ True,  True,  True,  True],
       [ True,  True,  True,  True],
       [ True,  True,  True,  True]])
>>> Rzx = qiskit.circuit.library.standard_gates.RZXGate(theta=np.pi)
>>> np.isclose(np.array(Rzx), -1j*np.kron(np.array(X), np.array(Z)))
array([[ True,  True,  True,  True],
       [ True,  True,  True,  True],
       [ True,  True,  True,  True],
       [ True,  True,  True,  True]])
```<hr>This is an automatic backport of pull request #13226 done by [Mergify](https://mergify.com).

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[coveralls]

Pull Request Test Coverage Report for Build 11069648430

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 20 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.003%) to 89.759%

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Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/expr.rs	1	94.02%
qiskit/transpiler/passes/synthesis/unitary_synthesis.py	2	88.39%
crates/qasm2/src/lex.rs	5	92.23%
crates/qasm2/src/parse.rs	12	97.15%

Totals
Change from base Build 11037032994:	-0.003%
Covered Lines:	66878
Relevant Lines:	74508

---

💛 - Coveralls