Update MIRI pin (#1828)

* Update MIRI

* Unpin MIRI

Author: tustvold

.github/workflows/miri.yaml

@@ -26,19 +26,15 @@ jobs:
   miri-checks:
     name: MIRI
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        arch: [amd64]
-        rust: [nightly-2022-01-17]
     steps:
       - uses: actions/checkout@v2
         with:
           submodules: true
       - name: Setup Rust toolchain
         run: |
-          rustup toolchain install ${{ matrix.rust }}
-          rustup default ${{ matrix.rust }}
-          rustup component add rustfmt clippy miri
+          rustup toolchain install nightly --component miri
+          rustup override set nightly
+          cargo miri setup
       - name: Run Miri Checks
         env:
           RUST_BACKTRACE: full