fix coveralls badge

README.md

@@ -2,7 +2,7 @@
 
 [![Build Status](https://api.cirrus-ci.com/github/c-ares/c-ares.svg?branch=main)](https://cirrus-ci.com/github/c-ares/c-ares)
 [![Windows Build Status](https://ci.appveyor.com/api/projects/status/aevgc5914tm72pvs/branch/main?svg=true)](https://ci.appveyor.com/project/c-ares/c-ares/branch/main)
-[![Coverage Status](https://coveralls.io/repos/github/c-ares/c-ares/badge.svg)](https://coveralls.io/github/c-ares/c-ares)
+[![Coverage Status](https://coveralls.io/repos/github/c-ares/c-ares/badge.svg?branch=main)](https://coveralls.io/github/c-ares/c-ares?branch=main)
 [![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/291/badge)](https://bestpractices.coreinfrastructure.org/projects/291)
 [![Fuzzing Status](https://oss-fuzz-build-logs.storage.googleapis.com/badges/c-ares.svg)](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=1&q=proj:c-ares)
 [![Bugs](https://sonarcloud.io/api/project_badges/measure?project=c-ares_c-ares&metric=bugs)](https://sonarcloud.io/summary/new_code?id=c-ares_c-ares)