Cargo.toml: bump MSRV to 1.75.0

Sync what we did in coreos/coreos-installer@d974fed

Author: HuijingHei

Cargo.toml

@@ -5,7 +5,7 @@ license = "Apache-2.0"
 version = "0.2.20"
 authors = ["Colin Walters <[email protected]>"]
 edition = "2021"
-rust-version = "1.70.0"
+rust-version = "1.75.0"
 
 include = ["src", "LICENSE", "Makefile", "systemd"]