ci: rustup --no-self-update and require MSRV checks

.github/workflows/main.yml

@@ -29,44 +29,19 @@ jobs:
     steps:
     - uses: actions/checkout@master
     - name: Install Rust
-      run: rustup update nightly && rustup default nightly
+      run: rustup update nightly --no-self-update && rustup default nightly
     - run: rustup target add ${{ matrix.target }}
     - run: rustup target add x86_64-unknown-linux-musl
     - run: cargo generate-lockfile
     - run: ./ci/run-docker.sh ${{ matrix.target }}
 
-  msrv:
-    name: Check MSRV
-    runs-on: ubuntu-latest
-    env:
-      RUSTFLAGS: # No need to check warnings on old MSRV, unset `-Dwarnings`
-    steps:
-    - uses: actions/checkout@master
-    - run: |
-        msrv="$(perl -ne 'print if s/rust-version\s*=\s*"(.*)"/\1/g' Cargo.toml)"
-        echo "MSRV: $msrv"
-        echo "MSRV=$msrv" >> "$GITHUB_ENV"
-    - name: Install Rust
-      run: rustup update "$MSRV" && rustup default "$MSRV"
-    - run: cargo build -p libm
-
-
-  rustfmt:
-    name: Rustfmt
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@master
-    - name: Install Rust
-      run: rustup update nightly && rustup default nightly && rustup component add rustfmt
-    - run: cargo fmt -- --check
-
   wasm:
     name: WebAssembly
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@master
     - name: Install Rust
-      run: rustup update nightly && rustup default nightly
+      run: rustup update nightly --no-self-update && rustup default nightly
     - run: rustup target add wasm32-unknown-unknown
     - run: cargo build --target wasm32-unknown-unknown
 
@@ -76,7 +51,7 @@ jobs:
     steps:
     - uses: actions/checkout@master
     - name: Install Rust
-      run: rustup update nightly && rustup default nightly
+      run: rustup update nightly --no-self-update && rustup default nightly
     - run: cargo build -p cb
 
   benchmarks:
@@ -85,16 +60,44 @@ jobs:
     steps:
     - uses: actions/checkout@master
     - name: Install Rust
-      run: rustup update nightly && rustup default nightly
+      run: rustup update nightly --no-self-update && rustup default nightly
     - run: cargo bench --all
 
+  msrv:
+    name: Check MSRV
+    runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: # No need to check warnings on old MSRV, unset `-Dwarnings`
+    steps:
+    - uses: actions/checkout@master
+    - run: |
+        msrv="$(perl -ne 'print if s/rust-version\s*=\s*"(.*)"/\1/g' Cargo.toml)"
+        echo "MSRV: $msrv"
+        echo "MSRV=$msrv" >> "$GITHUB_ENV"
+    - name: Install Rust
+      run: rustup update "$MSRV" --no-self-update && rustup default "$MSRV"
+    - run: cargo build -p libm
+
+  rustfmt:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: Install Rust
+      run: |
+        rustup update nightly --no-self-update
+        rustup default nightly
+        rustup component add rustfmt
+    - run: cargo fmt -- --check
+
   success:
     needs:
       - docker
-      - rustfmt
       - wasm
       - cb
       - benchmarks
+      - msrv
+      - rustfmt
     runs-on: ubuntu-latest
     # GitHub branch protection is exceedingly silly and treats "jobs skipped because a dependency
     # failed" as success. So we have to do some contortions to ensure the job fails if any of its