update rust toolchain to 1.69.0 (#9691)

# Description

This PR bumps the rust toolchain from 1.68.2 to 1.69.0 since 1.71.0 was
released 7/13/2023.

# User-Facing Changes
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rust-toolchain.toml

@@ -16,5 +16,4 @@ profile = "default"
 # use in nushell, we may opt to use the bleeding edge stable version of rust.
 # I believe rust is on a 6 week release cycle and nushell is on a 3 week release cycle.
 # So, every two nushell releases, this version number should be bumped by one.
-channel = "1.68.2"
-
+channel = "1.69.0"