Switch date-check to Rust 2021

No migrations were necessary.

Author: camelid

ci/date-check/Cargo.toml

@@ -2,7 +2,7 @@
 name = "date-check"
 version = "0.1.0"
 authors = ["Camelid <[email protected]>"]
-edition = "2018"
+edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html