Upgrade Rust to 1.52.0 (#17096)

* Upgrade Rust to 1.52.0
update nightly_version to newly pushed docker image
fix clippy lint errors
1.52 comes with grcov 0.8.0, include this version to script

* upgrade to Rust 1.52.1

* disabling Serum from downstream projects until it is upgraded to Rust 1.52.1

programs/vote/src/lib.rs

@@ -1,4 +1,4 @@
-#![cfg_attr(RUSTC_WITH_SPECIALIZATION, feature(specialization))]
+#![cfg_attr(RUSTC_WITH_SPECIALIZATION, feature(min_specialization))]
 #![allow(clippy::integer_arithmetic)]
 
 pub mod authorized_voters;