dev-dep: Upgrade solargraph gem to 0.46.0

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR upgrades the solargraph gem to 0.46.0, to avoid prompting by Neovim/CoC to upgrade to the latest gem version. For reference, see Upgrade solargraph gem to 0.45.0 (!93031 - merged)

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Changes since last version include:

- Ignore typecheck errors with @sg-ignore tag (#419)
- Strict checks report undefined method calls on variables (#553)
- Infer type from method arguments (#554)
- Return nil value for empty hover contents (#543)

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