Freeze nightly before regression (#20)

This commit is to be reverted once rust-lang/rust#104815 is fixed.

Author: baloo

.github/workflows/minimal-versions.yml

@@ -20,7 +20,7 @@ jobs:
       - uses: RustCrypto/actions/cargo-cache@master
       - uses: actions-rs/toolchain@v1
         with:
-          toolchain: nightly
+          toolchain: nightly-2022-11-21
           override: true
           profile: minimal
       - uses: RustCrypto/actions/cargo-hack-install@master