cdk diff always reports diff if resource has non-ASCII characters.

Reproduction Steps

import * as cdk from "@aws-cdk/core";
import * as codebuild from "@aws-cdk/aws-codebuild";

const app = new cdk.App();
const stack = new cdk.Stack(app, "stack1");
new codebuild.Project(stack, "FooProject", {
  buildSpec: codebuild.BuildSpec.fromObject({
    version: "0.2",
    phases: {
      build: {
        commands: ["echo こんにちは"], // "Hello" in Japanese
      },
    },
  }),
});

$ cdk --version
1.63.0 (build 7a68125)

$ cdk deploy stack1 --require-approval=never
stack1: deploying...
<snip>
 ✅  stack1

$ cdk diff stack1
Stack stack1
Resources
[~] AWS::CodeBuild::Project FooProject FooProject9FE653E4 
 └─ [~] Source
     └─ [~] .BuildSpec:
         ├─ [-] {
  "version": "0.2",
  "phases": {
    "build": {
      "commands": [
        "echo ?????"
      ]
    }
  }
}
         └─ [+] {
  "version": "0.2",
  "phases": {
    "build": {
      "commands": [
        "echo こんにちは"
      ]
    }
  }
}

What did you expect to happen?

cdk diff reports no diff, when resources are in sync.

What actually happened?

cdk diff always reports diff, even when resources are in sync.

Environment

• CLI Version : 1.63.0
• Framework Version: 1.63.0
• Node.js Version: v12.18.4
• OS : Linux (Docker container)
• Language (Version): all (I guess...)

Other

Guessing from its behavior, it seems like correct encoding(UTF-8?) is not specified while fetching current template from CloudFormation. So that the non-ASCII characters are converted to the "?" character and treated as if it is having diffs.

This is 🐛 Bug Report