fix(grammar): Fix syntax highlighting for Kernel.` method in Ruby grammar

[Sean0628]

Motivation

Closes #1470

The issue was that syntax highlighting breaks when using the Kernel.\` method in Ruby code. The grammar was incorrectly treating the backtick in this context as the start of an interpolated string literal, leading to incorrect tokenization and highlighting.

Implementation

To address this, the Ruby grammar was updated to properly distinguish between backtick string literals and the Kernel.` method calls. Specifically, the begin pattern for backticks was modified to include a negative lookbehind (?<!\\.), ensuring that only standalone backticks are treated as string delimiters.

(?<!…) — Negative Lookbehind. Matches if the provided pattern would not match the preceding characters, but does not advance the current position. The pattern must have a fixed length (unbounded quantifiers are not permitted).

ref. https://rbuckton.github.io/regexp-features/engines/oniguruma.html

Additionally, I added new test cases to cover both standard backtick strings and Kernel.\` method calls. These tests verify that the grammar correctly tokenizes each scenario, ensuring that backtick strings are recognized as interpolated strings, while Kernel.\` methods are handled without string interpretation.

Automated Tests

Unit tests were added as part of this change to ensure that both scenarios (standard backtick strings and Kernel.\` method calls) are correctly handled by the grammar.

Manual Tests

Before

After

[Sean0628]

I have signed the CLA!

[vinistock]

Nice. Thank you for the contribution!