rustup: rename HEAD branch to main

Author: rami3l

Formula/r/rustup.rb

@@ -4,7 +4,7 @@ class Rustup < Formula
   url "https://github.com/rust-lang/rustup/archive/refs/tags/1.28.2.tar.gz"
   sha256 "5987dcb828068a4a5e29ba99ab26f2983ac0c6e2e4dc3e5b3a3c0fafb69abbc0"
   license any_of: ["Apache-2.0", "MIT"]
-  head "https://github.com/rust-lang/rustup.git", branch: "master"
+  head "https://github.com/rust-lang/rustup.git", branch: "main"
 
   bottle do
     sha256 cellar: :any_skip_relocation, arm64_tahoe:   "64f4ef0c6a93f3f1261e7a83e5e1de535af07109777de50e699d7bc76c5e8e7c"