Never exit on errors during Linter test runs

Always set +exit_on_errors+ to false for Linter test runs,
even for test cases that should not cause errors, to avoid
stopping test runs and silencing (unexpected) error messages
during development.

Author: stomar

test/test_linter.rb

@@ -16,7 +16,7 @@
 
   it "can run ok" do
     Dir.chdir @md_ok
-    stdout, stderr = capture_io { Linter.new.run }
+    stdout, stderr = capture_io { Linter.new(exit_on_errors: false).run }
 
     stdout.must_equal @output_ok
   end