build: use msrv instead of toolchain file

Author: ctron

Cargo.toml

@@ -7,6 +7,7 @@ license = "Apache-2.0"
 readme = "README.md"
 description = "A quickstart project for using PatternFly with Yew"
 repository = "https://github.com/ctron/patternfly-yew-quickstart"
+rust-version = "1.90.0"
 
 [dependencies]
 browser-panic-hook = "0.2"