Enforce `gitlab:db:validate_config` in production

This is required to ensure that if migrations are "skipped"
are correctly skipped.

lib/tasks/gitlab/db/validate_config.rake

@@ -85,9 +85,13 @@ namespace :gitlab do
         warnings.unshift("Database config validation failure:")
 
         # Warn (for now) by default in production environment
-        if Gitlab::Utils.to_boolean(ENV['GITLAB_VALIDATE_DATABASE_CONFIG'], default: Gitlab.dev_or_test_env?)
+        if Gitlab::Utils.to_boolean(ENV['GITLAB_VALIDATE_DATABASE_CONFIG'], default: true)
+          warnings << "Use `export GITLAB_VALIDATE_DATABASE_CONFIG=0` to ignore this validation."
+
           raise warnings.join("\n")
         else
+          warnings << "Use `export GITLAB_VALIDATE_DATABASE_CONFIG=1` to enforce this validation."
+
           warn warnings.join("\n")
         end
       end

spec/lib/gitlab/database_spec.rb

@@ -270,9 +270,6 @@ RSpec.describe Gitlab::Database do
       before do
         skip_if_multiple_databases_not_setup
 
-        # This is currently required as otherwise the `Ci::Build.connection` == `Project.connection`
-        # ENV due to lib/gitlab/database/load_balancing/setup.rb:93
-        stub_env('GITLAB_USE_MODEL_LOAD_BALANCING', '1')
         # FF due to lib/gitlab/database/load_balancing/configuration.rb:92
         # Requires usage of `:request_store`
         stub_feature_flags(force_no_sharing_primary_model: true)

spec/tasks/gitlab/db/validate_config_rake_spec.rb

@@ -72,18 +72,23 @@ RSpec.describe 'gitlab:db:validate_config', :silence_stdout do
         expect { run_rake_task('gitlab:db:validate_config') }.to raise_error(match)
       end
 
-      it 'to stderr instead of exception for production' do
+      it 'for production' do
         allow(Gitlab).to receive(:dev_or_test_env?).and_return(false)
 
-        expect { run_rake_task('gitlab:db:validate_config') }.to output(match).to_stderr
+        expect { run_rake_task('gitlab:db:validate_config') }.to raise_error(match)
       end
 
-      it 'if GITLAB_VALIDATE_DATABASE_CONFIG is set' do
+      it 'if GITLAB_VALIDATE_DATABASE_CONFIG=1' do
         stub_env('GITLAB_VALIDATE_DATABASE_CONFIG', '1')
-        allow(Gitlab).to receive(:dev_or_test_env?).and_return(false)
 
         expect { run_rake_task('gitlab:db:validate_config') }.to raise_error(match)
       end
+
+      it 'to stderr if GITLAB_VALIDATE_DATABASE_CONFIG=0' do
+        stub_env('GITLAB_VALIDATE_DATABASE_CONFIG', '0')
+
+        expect { run_rake_task('gitlab:db:validate_config') }.to output(match).to_stderr
+      end
     end
 
     context 'when only main: is specified' do