Raise toolchain version for preserve_order to rust 1.46

Our indexmap dependency needs at least this version.

    error[E0658]: use of unstable library feature 'vec_drain_as_slice': recently added
        --> github.com-1ecc6299db9ec823/indexmap-1.8.0/src/map.rs:1182:30
         |
    1182 |         let iter = self.iter.as_slice().iter().map(Bucket::refs);
         |                              ^^^^^^^^

    error[E0658]: use of unstable library feature 'vec_drain_as_slice': recently added
       --> github.com-1ecc6299db9ec823/indexmap-1.8.0/src/set.rs:842:30
        |
    842 |         let iter = self.iter.as_slice().iter().map(Bucket::key_ref);
        |                              ^^^^^^^^

.github/workflows/ci.yml

@@ -33,7 +33,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [beta, stable, 1.45.0, 1.40.0, 1.38.0, 1.36.0]
+        rust: [beta, stable, 1.53.0, 1.46.0, 1.45.0, 1.40.0, 1.38.0, 1.36.0]
         os: [ubuntu]
         include:
           - rust: stable
@@ -44,14 +44,15 @@ jobs:
         with:
           toolchain: ${{matrix.rust}}
       - run: cargo check
-      - run: cargo check --features preserve_order
-        if: matrix.rust != '1.36.0'
-      - run: cargo check --manifest-path tests/crate/Cargo.toml --no-default-features --features alloc,preserve_order
-        if: matrix.rust != '1.36.0'
       - run: cargo check --features float_roundtrip
       - run: cargo check --features arbitrary_precision
       - run: cargo check --features raw_value
       - run: cargo check --features unbounded_depth
+      - run: cargo check --manifest-path tests/crate/Cargo.toml --no-default-features --features alloc
+      - run: cargo check --features preserve_order
+        if: matrix.rust != '1.45.0' && matrix.rust != '1.40.0' && matrix.rust != '1.38.0' && matrix.rust != '1.36.0'
+      - run: cargo check --manifest-path tests/crate/Cargo.toml --no-default-features --features alloc,preserve_order
+        if: matrix.rust != '1.45.0' && matrix.rust != '1.40.0' && matrix.rust != '1.38.0' && matrix.rust != '1.36.0'
       - name: Build without std
         run: |
           rustup target add aarch64-unknown-none
@@ -62,14 +63,6 @@ jobs:
               --features alloc
         if: matrix.rust == 'stable' && matrix.os == 'ubuntu'
 
-  nostd:
-    name: Rust 1.36.0
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - uses: dtolnay/rust-toolchain@1.36.0
-      - run: cargo check --manifest-path tests/crate/Cargo.toml --no-default-features --features alloc
-
   miri:
     name: Miri
     runs-on: ubuntu-latest