crate: exclude .github folder on publish

Cargo.toml

@@ -14,6 +14,7 @@ readme = "README.md"
 keywords = ["riscv", "sbi", "rustsbi"]
 categories = ["os", "embedded", "hardware-support", "no-std"]
 edition = "2021"
+exclude = ["/.github"]
 
 [dependencies]
 sbi-spec = "0.0.5-rc.2"