chore(ci): Fix logstash build (backport k260)

[loki-gh-app]

Backport bc418c4 from #18199

---

What this PR does / why we need it:

The logstash plugin build step in Github workflows failed https://github.com/grafana/loki/actions/runs/15814913050/job/44576897829

#7 [2/7] RUN gem install bundler:2.3.6
#7 4.152 ERROR:  Loading command: install (Gem::MissingSpecError)
#7 4.152 	Gem::MissingSpecError
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/specification.rb:1453:in `block in activate_dependencies'
#7 4.155 	org/jruby/RubyArray.java:1981:in `each'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/specification.rb:1439:in `activate_dependencies'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/specification.rb:1421:in `activate'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/core_ext/kernel_gem.rb:68:in `block in gem'
#7 4.155 	org/jruby/ext/thread/Mutex.java:174:in `synchronize'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/core_ext/kernel_gem.rb:68:in `gem'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/core_ext/kernel_require.rb:73:in `require'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/request.rb:2:in `<main>'
#7 4.155 	org/jruby/RubyKernel.java:1187:in `require'
#7 4.155 	org/jruby/RubyKernel.java:1216:in `require_relative'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/remote_fetcher.rb:3:in `<main>'
#7 4.155 	org/jruby/RubyKernel.java:1187:in `require'
#7 4.155 	org/jruby/RubyKernel.java:1216:in `require_relative'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/spec_fetcher.rb:2:in `<main>'
#7 4.155 	org/jruby/RubyKernel.java:1187:in `require'
#7 4.155 	org/jruby/RubyKernel.java:1216:in `require_relative'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/dependency_installer.rb:6:in `<main>'
#7 4.155 	org/jruby/RubyKernel.java:1187:in `require'
#7 4.155 	org/jruby/RubyKernel.java:1216:in `require_relative'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/commands/install_command.rb:4:in `<main>'
#7 4.155 	org/jruby/RubyKernel.java:1187:in `require'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/core_ext/kernel_require.rb:85:in `require'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/command_manager.rb:228:in `load_and_instantiate'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/command_manager.rb:135:in `[]'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/command_manager.rb:201:in `find_command'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/command_manager.rb:183:in `process_args'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/command_manager.rb:149:in `run'
#7 4.155 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/gem_runner.rb:51:in `run'
#7 4.155 	/usr/share/logstash/vendor/jruby/bin/jgem:21:in `<main>'
#7 4.155 	org/jruby/RubyKernel.java:1223:in `load'
#7 4.155 	/usr/share/logstash/vendor/jruby/bin/gem:4:in `<main>'
#7 4.248 ERROR:  While executing gem ... (NoMethodError)
#7 4.248     undefined method `deprecated?' for nil:NilClass
#7 4.251 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/command_manager.rb:184:in `process_args'
#7 4.251 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/command_manager.rb:149:in `run'
#7 4.251 	/usr/share/logstash/vendor/jruby/lib/ruby/stdlib/rubygems/gem_runner.rb:51:in `run'
#7 4.251 	/usr/share/logstash/vendor/jruby/bin/jgem:21:in `<main>'
#7 4.251 	org/jruby/RubyKernel.java:1223:in `load'
#7 4.251 	/usr/share/logstash/vendor/jruby/bin/gem:4:in `<main>'
#7 ERROR: process "/bin/sh -c gem install bundler:2.3.6" did not complete successfully: exit code: 1