Update munit-cats-effect to 2.0.0-M4 in main

Author: http4s-steward[bot]

build.sbt

@@ -14,7 +14,7 @@ val http4sVersion = "1.0.0-M39"
 val scalacheckXmlVersion = "0.1.0"
 val scalaXmlVersion = "2.1.0"
 val munitVersion = "1.0.0-M8"
-val munitCatsEffectVersion = "2.0.0-M3"
+val munitCatsEffectVersion = "2.0.0-M4"
 
 lazy val scalaXml2 = project
   .in(file("scala-xml-2"))