Bump govuk_test that includes fixed version of Brakeman

Brakeman has an issue that's causing builds to fail. [1]

1 presidentbeef/brakeman#1607

Gemfile.lock

@@ -71,7 +71,7 @@ GEM
       rack (>= 0.9.0)
     binding_of_caller (0.8.0)
       debug_inspector (>= 0.0.1)
-    brakeman (4.10.1)
+    brakeman (5.0.2)
     builder (3.2.4)
     capybara (3.35.3)
       addressable
@@ -132,8 +132,8 @@ GEM
       sprockets (< 4)
     govuk_template (0.26.0)
       rails (>= 3.1)
-    govuk_test (2.2.0)
-      brakeman (~> 4.6)
+    govuk_test (2.3.0)
+      brakeman (>= 5.0.2)
       capybara
       puma
       selenium-webdriver (>= 3.142)
@@ -194,7 +194,7 @@ GEM
     multipart-post (2.1.1)
     netrc (0.11.0)
     nio4r (2.5.7)
-    nokogiri (1.11.4)
+    nokogiri (1.11.7)
       mini_portile2 (~> 2.5.0)
       racc (~> 1.4)
     null_logger (0.0.1)
@@ -208,7 +208,7 @@ GEM
       coderay (~> 1.1)
       method_source (~> 1.0)
     public_suffix (4.0.6)
-    puma (5.3.1)
+    puma (5.3.2)
       nio4r (~> 2.0)
     racc (1.5.2)
     rack (2.2.3)
@@ -325,7 +325,7 @@ GEM
     unicorn (5.8.0)
       kgio (~> 2.6)
       raindrops (~> 0.7)
-    webdrivers (4.4.1)
+    webdrivers (4.6.0)
       nokogiri (~> 1.6)
       rubyzip (>= 1.3.0)
       selenium-webdriver (>= 3.0, < 4.0)