gix-date: bump MSRV to Rust 1.70

The bump to Rust 1.70 (released over 1 year ago) is needed since that's
Jiff current MSRV. This doesn't bump the MSRV of the broader gitoxide
project, however, so this is probably wrong or incomplete.

gix-date/Cargo.toml

@@ -7,7 +7,7 @@ description = "A crate of the gitoxide project parsing dates the way git does"
 authors = ["Sebastian Thiel <sebastian.thiel@icloud.com>"]
 edition = "2021"
 include = ["src/**/*", "LICENSE-*"]
-rust-version = "1.65"
+rust-version = "1.70"
 
 [lib]
 doctest = false