Do not raise when validating variables expression

lib/gitlab/ci/config/entry/policy.rb

@@ -47,7 +47,7 @@ module Gitlab
 
                 statements.each do |statement|
                   unless statement.valid?
-                    errors.add(:variables, "Invalid expression #{statement.inspect}")
+                    errors.add(:variables, "Invalid expression syntax")
                   end
                 end
               end

lib/gitlab/ci/pipeline/expression/statement.rb

@@ -37,10 +37,6 @@ module Gitlab
             evaluate.present?
           end
 
-          def inspect
-            "syntax: #{@lexer.lexemes.join(' ')}"
-          end
-
           def valid?
             parse_tree.is_a?(Lexeme::Base)
           rescue StatementError

spec/lib/gitlab/ci/config/entry/policy_spec.rb

@@ -104,7 +104,15 @@ describe Gitlab::Ci::Config::Entry::Policy do
       let(:config) { { variables: ['$MY_VAR =='] } }
 
       it 'reports an error about invalid statement' do
-        expect(entry.errors).to include /invalid expression syntax: variable equals/
+        expect(entry.errors).to include /invalid expression syntax/
+      end
+    end
+
+    context 'when specifying invalid variables expressions token' do
+      let(:config) { { variables: ['$MY_VAR == 123'] } }
+
+      it 'reports an error about invalid statement' do
+        expect(entry.errors).to include /invalid expression syntax/
       end
     end