CI: Run the schemars job directly using cargo

The `Schemars` job calls the `run_task.sh` script only to do a single
invocation of `cargo test` - just call cargo directly.

.github/workflows/rust.yml

@@ -260,8 +260,8 @@ jobs:
         uses: actions/checkout@v4
       - name: "Select toolchain"
         uses: dtolnay/rust-toolchain@stable
-      - name: "Run test script"
-        run: ./contrib/run_task.sh schemars
+      - name: "Run schemars test"
+        run: cd hashes/extended_tests/schemars && cargo test
 
   Kani:
     name: Kani codegen - stable toolchain

contrib/run_task.sh

@@ -100,11 +100,6 @@ main() {
 	    do_asan
 	    ;;
 
-	schemars)
-            # hashes crate only.
-	    do_schemars
-	    ;;
-
         *)
             err "Error: unknown task $task"
             ;;
@@ -264,13 +259,6 @@ do_bench() {
     done
 }
 
-# This is only relevant for hashes.
-do_schemars() {
-    pushd "$REPO_DIR/hashes/extended_tests/schemars" > /dev/null
-    cargo test
-    popd > /dev/null
-}
-
 # Note we do not use the recent lock file or `--locked` when running the wasm tests.
 do_wasm() {
     pushd "$REPO_DIR/hashes" > /dev/null