fix(ci/test): slow down the test speed

Author: pan93412

.github/workflows/ci.yml

@@ -30,10 +30,13 @@ jobs:
                   toolchain: nightly
                   override: true
             - uses: taiki-e/install-action@nextest
+            - uses: actions-rs/cargo@v1
+              with:
+                  command: build
             - uses: actions-rs/cargo@v1
               with:
                   command: nextest
-                  args: run
+                  args: run -j1
 
     doc-test:
         name: Cargo doctest