fix(mise): use github backend for sccache instead of deprecated ubi

The ubi backend installed a broken sccache binary on linux/amd64 that
did not support RUSTC_WRAPPER mode. The github backend properly extracts
the release tarball and provides the correct binary.

Author: drew

mise.toml

@@ -15,7 +15,7 @@ kubectl = "1.35.1"
 uv = "0.10.2"
 protoc = "29.6"
 helm = "4.1.1"
-"ubi:mozilla/sccache" = "0.14.0"
+"github:mozilla/sccache" = "0.14.0"
 
 [env]
 _.path = ["{{config_root}}/scripts/bin"]