Check only (no longer test) at the MSRV

Adjust CI so we only run a check the main crate at the MSRV (1.23),
running tests only at the MSRV of test dependencies. This allows us to
keep CI passing without increasing `glob`'s MSRV to match that of `libc`
(which since recently is 1.63.0) or other test dependencies.

Additionally, set `rust-version` in Cargo.toml.

.github/workflows/rust.yml

@@ -16,7 +16,7 @@ jobs:
           - stable
           - beta
           - nightly
-          - 1.23.0
+          - 1.63.0 # MSRV of test dependencies
         os:
           - macos-11
           - windows-2022
@@ -33,3 +33,18 @@ jobs:
 
     - name: Tests
       run: cargo +${{ matrix.channel }} test --all
+
+  msrv:
+    name: "Check with the MSRV"
+    runs-on: ubuntu-22.04
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+
+    - name: Update rust
+      run: |
+        rustup default 1.23.0
+        rustup update --no-self-update
+
+    - name: Tests
+      run: cargo check

Cargo.toml

@@ -11,6 +11,7 @@ description = """
 Support for matching file paths against Unix shell style patterns.
 """
 categories = ["filesystem"]
+rust-version = "1.23.0"
 
 [dev-dependencies]
 # FIXME: Replace it with `tempfile` once we bump up MSRV.