Delete support for compilers without NonZero integer types

.github/workflows/ci.yml

@@ -83,18 +83,12 @@ jobs:
       - run: cd serde && cargo build
 
   more:
-    name: Rust ${{matrix.rust}}
+    name: Rust 1.28.0
     runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
-      matrix:
-        rust: [1.27.0, 1.28.0]
     timeout-minutes: 45
     steps:
       - uses: actions/checkout@v3
-      - uses: dtolnay/rust-toolchain@master
-        with:
-          toolchain: ${{matrix.rust}}
+      - uses: dtolnay/rust-toolchain@1.28.0
         # Work around failing to parse manifest because editions are unstable.
       - run: sed -i /test_suite/d Cargo.toml
       - run: cd serde && cargo build --no-default-features