chore(ci): Ensure we test minimum features

I was working to drop the active features across all crates, so that
when cargo unified them during `--workspace`, we'd get this for free.
Alas, it looks like its not happening.

.github/workflows/ci.yml

@@ -68,6 +68,9 @@ jobs:
       run: make test-${{matrix.features}}
     - name: Test (benches)
       run: make test-${{matrix.features}} ARGS='--workspace --benches'
+    - name: Test (ultra-minimal)
+      if: matrix.build == 'minimal'
+      run: make test-minimal ARGS='--manifest-path Cargo.toml'
   check:
     name: Check
     runs-on: ubuntu-latest

.github/workflows/rust-next.yml

@@ -55,6 +55,9 @@ jobs:
       run: make test-${{matrix.features}}
     - name: Test (benches)
       run: make test-${{matrix.features}} ARGS='--workspace --benches'
+    - name: Test (ultra-minimal)
+      if: matrix.build == 'minimal'
+      run: make test-minimal ARGS='--manifest-path Cargo.toml'
   rustfmt:
     name: rustfmt
     strategy: