undefined method 'Pathname' for class RBS::EnvironmentLoader (NoMethodError) when running tests for version 3.10.4

When running tests for version 3.4.10 against ruby version 3.4.8 I get the following errors during the tests:

/build/ruby-rbs/src/rbs/lib/rbs/environment_loader.rb:26:in '<class:EnvironmentLoader>': undefined method 'Pathname' for class RBS::EnvironmentLoader (NoMethodError)

    DEFAULT_CORE_ROOT = Pathname(_ = __dir__) + "../../core"
                        ^^^^^^^^
        from /build/ruby-rbs/src/rbs/lib/rbs/environment_loader.rb:4:in '<module:RBS>'
        from /build/ruby-rbs/src/rbs/lib/rbs/environment_loader.rb:3:in '<top (required)>'
        from <internal:/usr/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require'
        from <internal:/usr/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require'
        from /build/ruby-rbs/src/rbs/lib/rbs.rb:29:in '<top (required)>'
        from <internal:/usr/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require'
        from <internal:/usr/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require'
        from /build/ruby-rbs/src/rbs/test/test_helper.rb:8:in '<top (required)>'
        from <internal:/usr/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require'
        from <internal:/usr/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require'
        from /build/ruby-rbs/src/rbs/test/rbs/ancestor_builder_test.rb:1:in '<top (required)>'
        from <internal:/usr/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require'
        from <internal:/usr/lib/ruby/3.4.0/rubygems/core_ext/kernel_require.rb>:136:in 'Kernel#require'
        from /usr/lib/ruby/gems/3.4.0/gems/rake-13.3.1/lib/rake/rake_test_loader.rb:21:in 'block in <main>'
        from /usr/lib/ruby/gems/3.4.0/gems/rake-13.3.1/lib/rake/rake_test_loader.rb:6:in 'Array#select'
        from /usr/lib/ruby/gems/3.4.0/gems/rake-13.3.1/lib/rake/rake_test_loader.rb:6:in '<main>'
rake aborted!
Command failed with status (1)

From my understanding the issue is a missing require 'pathname' in https://github.com/ruby/rbs/blob/v3.10.4/lib/rbs/environment_loader.rb before line 26.

I know this is an old version but as far as I can see this issue also wasn't fixed in the latest version and for no I'm stuck on the 3.x version branch.

Start with lib/rbs/environment_loader.rb around line 26 and reproduce the failure through the test setup referenced by test/test_helper.rb. Verify the environment loader can load on Ruby 3.4 and that the test suite proceeds without the Pathname NoMethodError.