Upgrade to rspec-rails 6

This prevents us from hitting some incompatibility issues between Ruby
3.1 and Ruby 3.2

rspec/rspec-mocks#1513

Gemfile

@@ -122,7 +122,7 @@ group :development, :test do
   gem "pry-byebug"
 
   # Testing framework
-  gem "rspec-rails", "~> 5.1"
+  gem "rspec-rails", "~> 6.0"
 
   gem "cypress-on-rails", "~> 1.13"
   gem "database_cleaner-active_record"

Gemfile.lock

@@ -420,17 +420,17 @@ GEM
     rspec-expectations (3.12.0)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.12.0)
-    rspec-mocks (3.12.0)
+    rspec-mocks (3.12.5)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.12.0)
-    rspec-rails (5.1.2)
-      actionpack (>= 5.2)
-      activesupport (>= 5.2)
-      railties (>= 5.2)
-      rspec-core (~> 3.10)
-      rspec-expectations (~> 3.10)
-      rspec-mocks (~> 3.10)
-      rspec-support (~> 3.10)
+    rspec-rails (6.0.1)
+      actionpack (>= 6.1)
+      activesupport (>= 6.1)
+      railties (>= 6.1)
+      rspec-core (~> 3.11)
+      rspec-expectations (~> 3.11)
+      rspec-mocks (~> 3.11)
+      rspec-support (~> 3.11)
     rspec-support (3.12.0)
     rswag-specs (2.8.0)
       activesupport (>= 3.1, < 7.1)
@@ -674,7 +674,7 @@ DEPENDENCIES
   rails-controller-testing (~> 1.0.5)
   ransack
   rspec-default_http_header (~> 0.0.6)
-  rspec-rails (~> 5.1)
+  rspec-rails (~> 6.0)
   rswag-specs (~> 2.8)
   rubocop-govuk (>= 4.8)
   rubyzip (~> 2.3, >= 2.3.0)