development-dependency: bump solargraph from 0.42.1 to 0.42.3

Bumps solargraph from 0.42.1 to 0.42.3.

Changelog

Sourced from solargraph's changelog.

0.42.3 - June 14, 2021

• Require 'pathname' for Library

0.42.2 - June 14, 2021

• Improve download-core command output
• Ignore missing requests to client responses
• Add automatically required gems to YardMap
• Use closures to identify local variables

Commits

• 8e1318e Require 'pathname' for Library
• b55d6a8 Release date
• e8610a6 Accept undefined from extra_return_type
• d13bbe5 Enumerable #detect and #find core fills
• 9d6b58f Start server request IDs at 1
• 7cbacb4 Bench description update
• 021c2f6 Update backport gem
• a69c528 Reduce error output
• de113ab Move Localized to LocalVariable
• 5348a99 Deeper local variable detection
• Additional commits viewable in compare view

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