chore: allow miri to use latest nightly once again

This reverts [#4825], which was to address Miri being broken on the latest nightly, possibly due to an issue in rustup.

Rustup issue: rust-lang/rustup#3031

[#4825]: #4825

.github/workflows/ci.yml

@@ -195,7 +195,7 @@ jobs:
       - name: Install Rust ${{ env.rust_nightly }}
         uses: actions-rs/toolchain@v1
         with:
-          toolchain: nightly-2022-07-10
+          toolchain: nightly
           components: miri
           override: true
       - uses: Swatinem/rust-cache@v1