QubitUnitary docstring link fix

[isaacdevlugt]

Context:

Description of the Change: Link fix to one_qubit_decomposition

Benefits: Link works

Possible Drawbacks: Absolutely none—zip—zilch—zéro

Related GitHub Issues:

[github-actions]

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

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.60%. Comparing base (1e24270) to head (5c155f7).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6745   +/-   ##
=======================================
  Coverage   99.60%   99.60%           
=======================================
  Files         475      475           
  Lines       45121    45121           
=======================================
  Hits        44944    44944           
  Misses        177      177           

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