rust-toolchain: use 1.72.0, same as CI (#5256)

Switches everyone without an `rustup override` to 1.72.0.

Code changes required already done in #5255.
Depends on neondatabase/build#65.

rust-toolchain.toml

@@ -1,5 +1,5 @@
 [toolchain]
-channel = "1.71.0"
+channel = "1.72.0"
 profile = "default"
 # The default profile includes rustc, rust-std, cargo, rust-docs, rustfmt and clippy.
 # https://rust-lang.github.io/rustup/concepts/profiles.html