fix badges in README

Now that tests actually pass again, update the status badge to show the
correct status. Also removes the codecov badge since we explicitly
disable coverage in our tests

README.md

@@ -1,4 +1,4 @@
-# Cthulhu.jl <a href="https://github.com/JuliaDebug/Cthulhu.jl/actions?query=workflow%3A%22CI%22+branch%3Amaster"><img src="https://github.com/JuliaDebug/Cthulhu.jl/workflows/CI/badge.svg"></a> <a href="https://codecov.io/gh/JuliaDebug/Cthulhu.jl"><img src="https://codecov.io/github/JuliaDebug/Cthulhu.jl/coverage.svg"></a>
+# Cthulhu.jl [![CI](https://github.com/JuliaDebug/Cthulhu.jl/actions/workflows/CI.yml/badge.svg)](https://github.com/JuliaDebug/Cthulhu.jl/actions/workflows/CI.yml)
 
 *The slow descent into madness*