test(deps): update dependency bundler to v2.5.18

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
bundler (source, changelog)	2.5.17 -> 2.5.18

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Release Notes

rubygems/rubygems (bundler)

v2.5.18

Compare Source

Enhancements:

• Don't remove existing platform gems when PLATFORMS section is badly indented #​7916

Bug fixes:

• Fix error message when Bundler refuses to install due to frozen being set without a lockfile #​7955
• Fix several issues with the --prefer-local flag #​7951
• Restore support for passing relative paths to git: sources #​7950
• Regenerate previous git application caches that didn't include bare repos #​7926
• Fix bundle update <indirect_dep> failing to upgrade when versions present in two different sources #​7915

Documentation:

• Change new gem README template to have copyable code blocks #​7935

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