build-unit-test-docker: eslint-plugin-json: pin to v3.1.0

The new v4.0.0 release does not work with an error like this:
```
Error: ESLint configuration in --config ยป plugin:json/recommended-with-comments is invalid:
	- Unexpected top-level property "files".
```
Pin eslint-plugin-json to v3.1.0 to solve this.

Change-Id: I773c9c0bda3b87cca92e69089ea37fb20f563ab9
Signed-off-by: Xinnan Xie <xiexinnan@bytedance.com>
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index 2beecba..3011c2f 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -871,7 +871,7 @@
         requests
 
 RUN npm install -g \
-        eslint@v8.56.0 eslint-plugin-json@latest \
+        eslint@v8.56.0 eslint-plugin-json@v3.1.0 \
         markdownlint-cli@latest \
         prettier@latest
 """