Do not exclude fuzz target when running cargo-hack

The fuzz target is not a member of the workspace, which triggers a
warning.

.github/workflows/features.yml

@@ -15,4 +15,4 @@ jobs:
       - name: Install cargo-hack
         run: cargo install cargo-hack
       - name: Build one feature at a time
-        run: cargo hack build --each-feature --workspace --exclude fuzz --exclude harness_client
+        run: cargo hack build --each-feature --workspace --exclude harness_client