chore: Bump MSRV to 1.73 and only check the library build for msrv

The test end up depending on crates requiring more recent rust, but for
msrv really only the library itself is important. Also bump to 1.73 as
that's the minimal required for the jsonwebtoken dependency

Author: sjoerdsimons

.github/workflows/ci.yml

@@ -28,16 +28,25 @@ jobs:
           components: clippy
       - run: cargo clippy --all-targets --all-features -- -D warnings
 
+  msrv:
+    name: Minimal rust version
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@master
+        with:
+            toolchain: "1.73"
+      - name: Build System Info
+        run: cargo build --lib --all-features
+
   tests:
     name: Tests
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        build: [pinned, stable, nightly]
+        build: [stable, nightly]
         include:
-        - build: pinned
-          os: ubuntu-22.04
-          rust: 1.68.0
         - build: stable
           os: ubuntu-22.04
           rust: stable