bump rust-toolchain to 1.70.0 (#10113)

# Description

This PR bumps the rust-toolchain to 1.70.0 since 1.72.0 was released
today.

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rust-toolchain.toml

@@ -16,4 +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 = "1.69.0"
+channel = "1.70.0"