Update gitlab-labkit to 0.4.2

This relaxes the gRPC version so that it can be updated. Also adds
cache support for distributed tracing.

Full release notes:
https://gitlab.com/gitlab-org/labkit-ruby/-/tags

Gemfile

@@ -283,7 +283,7 @@ gem 'sentry-raven', '~> 2.9'
 gem 'premailer-rails', '~> 1.9.7'
 
 # LabKit: Tracing and Correlation
-gem 'gitlab-labkit', '~> 0.3.0'
+gem 'gitlab-labkit', '~> 0.4.2'
 
 # I18n
 gem 'ruby_parser', '~> 3.8', require: false

Gemfile.lock

@@ -312,10 +312,10 @@ GEM
     gitaly-proto (1.37.0)
       grpc (~> 1.0)
     github-markup (1.7.0)
-    gitlab-labkit (0.3.0)
+    gitlab-labkit (0.4.2)
       actionpack (~> 5)
       activesupport (~> 5)
-      grpc (~> 1.19.0)
+      grpc (~> 1.19)
       jaeger-client (~> 0.10)
       opentracing (~> 0.4)
     gitlab-markup (1.7.0)
@@ -1098,7 +1098,7 @@ DEPENDENCIES
   gettext_i18n_rails_js (~> 1.3)
   gitaly-proto (~> 1.37.0)
   github-markup (~> 1.7.0)
-  gitlab-labkit (~> 0.3.0)
+  gitlab-labkit (~> 0.4.2)
   gitlab-markup (~> 1.7.0)
   gitlab-sidekiq-fetcher (= 0.5.1)
   gitlab-styles (~> 2.7)