Fix hyperlinks in random_ray.rst

[yardasol]

Description

The section of the theory manual on the Random Ray method has several hyperlinks that do not go anywhere. The links themselves are present in the source file, but a small repeated syntax error made them not render correctly when built with sphinx. This PR fixes the syntax error and makes the hyperlinks work as intended

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 15) on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

[jtramm]

LGTM! Thanks @yardasol for making these corrections!