Only check library target against MSRV

Author: djc

.github/workflows/rust.yml

@@ -20,9 +20,6 @@ jobs:
           - os: ubuntu-latest
             rust: beta
             features: --all-features
-          - os: ubuntu-latest
-            rust: 1.58
-            features: --features improved_unicode
           - os: ubuntu-latest
             rust: stable
             features: --all-features
@@ -66,6 +63,20 @@ jobs:
           command: test
           args: --workspace ${{ matrix.features }} ${{ matrix.target }}
 
+  msrv:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: "1.58"
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: check
+          args: --lib --all-features
+
   lint:
     runs-on: ubuntu-latest
     steps: