README: fix GitHub Actions badge url and query (#52)

Signed-off-by: Koichi Shiraishi <zchee.io@gmail.com>

README.md

@@ -1,7 +1,7 @@
 # Envconfig
 
 [![GoDoc](https://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)](https://pkg.go.dev/mod/github.com/sethvargo/go-envconfig)
-[![GitHub Actions](https://img.shields.io/github/workflow/status/sethvargo/go-envconfig/Test?style=flat-square)](https://github.com/sethvargo/go-envconfig/actions?query=workflow%3ATest)
+[![GitHub Actions](https://img.shields.io/github/workflow/status/sethvargo/go-envconfig/unit/main?style=flat-square)](https://github.com/sethvargo/go-envconfig/actions?query=branch%3Amain+-event%3Aschedule)
 
 Envconfig populates struct field values based on environment variables or
 arbitrary lookup functions. It supports pre-setting mutations, which is useful