test: run change refresh doctype fixture in CI

The change refresh modifier example used a .test.mdl suffix, so the doctype
fixture runner skipped it even though review feedback expected it to be part of
CI coverage.

Rename the fixture to .mdl and update the proposal reference so the existing
doctype integration test discovers the example.

Tests:
- make build
- ./bin/mxcli check mdl-examples/doctype-tests/change_refresh_modifier.mdl
- go test ./mdl/executor -run 'ChangeRefresh|RefreshInClient' -count=1
- make test

Author: hjothamendix

docs/11-proposals/PROPOSAL_microflow_change_refresh_modifier.md

@@ -21,7 +21,7 @@ The `refresh` modifier maps directly to `ChangeObjectAction.RefreshInClient`. Om
 
 ## Tests And Examples
 
-`mdl-examples/doctype-tests/change_refresh_modifier.test.mdl` demonstrates both forms. Go tests cover formatter output, parser behavior, and builder serialization.
+`mdl-examples/doctype-tests/change_refresh_modifier.mdl` demonstrates both forms. Go tests cover formatter output, parser behavior, and builder serialization.
 
 ## Open Questions