fix: update rust toolchain version (#2047)

## What ❔

- Update rust version

## Why ❔

- Last PR broke rust #2044

## Checklist

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- [x] PR title corresponds to the body of PR (we generate changelog
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- [x] Tests for the changes have been added / updated.
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- [x] Code has been formatted via `zk fmt` and `zk lint`.
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zk_toolbox/rust-toolchain

@@ -1 +1 @@
-stable-1.78.0
+1.78.0