display badge for master branch (#7344)

Author: jangorecki

README.md

@@ -3,7 +3,7 @@
 
 <!-- badges: start -->
 [![CRAN status](https://badges.cranchecks.info/flavor/release/data.table.svg)](https://cran.r-project.org/web/checks/check_results_data.table.html)
-[![R-CMD-check](https://github.com/Rdatatable/data.table/workflows/R-CMD-check/badge.svg)](https://github.com/Rdatatable/data.table/actions)
+[![R-CMD-check](https://github.com/Rdatatable/data.table/actions/workflows/R-CMD-check.yaml/badge.svg?branch=master)](https://github.com/Rdatatable/data.table/actions)
 [![Codecov test coverage](https://codecov.io/github/Rdatatable/data.table/coverage.svg?branch=master)](https://app.codecov.io/github/Rdatatable/data.table?branch=master)
 [![GitLab CI build status](https://gitlab.com/Rdatatable/data.table/badges/master/pipeline.svg)](https://rdatatable.gitlab.io/data.table/web/checks/check_results_data.table.html)
 [![downloads](https://cranlogs.r-pkg.org/badges/data.table)](https://www.rdocumentation.org/trends)