Add a min-versions run to the CI

This is more exhaustive than the min-versions-shallow run that only
downgrades direct dependencies.

.github/workflows/exhaustive.yml

@@ -26,7 +26,7 @@ jobs:
     - run: cargo --locked nextest run --workspace --all-features
     - run: cargo --locked test --workspace --doc --all-features
 
-  min-versions:
+  min-versions-shallow:
     name: cargo test --shallow-minimal-versions
     runs-on: ubuntu-latest
     steps:
@@ -55,6 +55,23 @@ jobs:
     - run: cargo --locked nextest run --workspace --all-features
     - run: cargo --locked test --workspace --doc --all-features
 
+  min-versions:
+    name: cargo test minimal-versions
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: actions-rust-lang/setup-rust-toolchain@v1
+      with: { toolchain: nightly }
+    - name: Update to minimal versions
+      run:
+        cargo update -Z minimal-versions
+    - uses: actions-rust-lang/setup-rust-toolchain@v1
+      with: { toolchain: stable }
+    - uses: taiki-e/install-action@v2
+      with: { tool: cargo-nextest }
+    - run: cargo --locked nextest run --workspace --all-features
+    - run: cargo --locked test --workspace --doc --all-features
+
   check-features:
     name: cargo hack check --feature-powerset
     runs-on: ubuntu-latest