Separate build and test CI jobs

Our dev dependencies have updated their minimum supported Rust
version (MSRV), so we now only check that the library builds on Rust
1.56. Tests are run on multiple Rust versions, as usual.

The MSRV is now also documented in the Cargo.toml file.

.github/workflows/build.yml

@@ -18,7 +18,6 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.56
           - stable
           - nightly
         os:
@@ -47,6 +46,22 @@ jobs:
         if: matrix.rust == 'nightly'
         run: cargo check --all-targets
 
+  msrv:
+    name: Build MSRV
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Install Rust
+        run: rustup default 1.56
+
+      - uses: Swatinem/rust-cache@v2
+
+      - name: Build
+        run: cargo build
+
   build-documentation:
     name: Build documentation
     runs-on: ubuntu-latest

Cargo.toml

@@ -17,6 +17,7 @@ keywords = ["random", "text", "markov", "typography"]
 categories = ["text-processing"]
 license = "MIT"
 edition = "2021"
+rust-version = "1.56"
 
 [dependencies]
 rand = {version = "0.8.5", default-features = false, features = ["alloc"]}