Try pinning nightly version

Author: Amanieu

.github/workflows/main.yml

@@ -15,7 +15,7 @@ jobs:
     steps:
     - uses: actions/checkout@master
     - name: Install Rust
-      run: rustup update nightly && rustup default nightly
+      run: rustup update nightly-2021-11-27 && rustup default nightly-2021-11-27
     - run: ci/style.sh
 
   docs:
@@ -25,7 +25,7 @@ jobs:
     steps:
     - uses: actions/checkout@master
     - name: Install Rust
-      run: rustup update nightly && rustup default nightly
+      run: rustup update nightly-2021-11-27 && rustup default nightly-2021-11-27
     - run: ci/dox.sh
       env:
         CI: 1
@@ -45,7 +45,7 @@ jobs:
     steps:
     - uses: actions/checkout@master
     - name: Install Rust
-      run: rustup update nightly && rustup default nightly
+      run: rustup update nightly-2021-11-27 && rustup default nightly-2021-11-27
     - run: cargo test --manifest-path crates/stdarch-verify/Cargo.toml
 
   env_override:
@@ -55,7 +55,7 @@ jobs:
     steps:
     - uses: actions/checkout@master
     - name: Install Rust
-      run: rustup update nightly && rustup default nightly
+      run: rustup update nightly-2021-11-27 && rustup default nightly-2021-11-27
     - run: RUST_STD_DETECT_UNSTABLE=avx cargo test --features=std_detect_env_override --manifest-path crates/std_detect/Cargo.toml env_override_no_avx
 
   test:
@@ -174,18 +174,18 @@ jobs:
         submodules: recursive
     - name: Install Rust (rustup)
       run: |
-        rustup update nightly --no-self-update
-        rustup default nightly
+        rustup update nightly-2021-11-27 --no-self-update
+        rustup default nightly-2021-11-27
       if: matrix.os != 'macos-latest'
     - name: Install Rust (macos)
       run: |
         curl https://sh.rustup.rs | sh -s -- -y --default-toolchain nightly
         echo "$HOME/.cargo/bin" >> $GITHUB_PATH
-        rustup update nightly --no-self-update
-        rustup default nightly
+        rustup update nightly-2021-11-27 --no-self-update
+        rustup default nightly-2021-11-27
       if: matrix.os == 'macos-latest'
     - run: |
-        rustup default nightly
+        rustup default nightly-2021-11-27
         rustup target add ${{ matrix.target }}
       if: "!endsWith(matrix.target, 'emulated')"
     - name: Setup (aarch64-apple-darwin)