[aws-lambda-python] Building fails because rsync does not exist in SAM build image for Python 3.8

[jarikujansuu]

PythonFunction tries to run rsync on build container but SAM build image for Python 3.8 doesn't have it. Default 3.7 image would have it.

Reproduction Steps

const app = new App();

class FoobarStack extends Stack {
  constructor(scope: Construct, id: string)  {
    super(scope, id);
    new PythonFunction(this, 'Foobar', {
      entry: './lambda/foobar',
      runtime: Runtime.PYTHON_3_8,
    })
  }
}

new FoobarStack(app, 'foobar');

...and then lambda/foobar directory with index.py and empty requirements.txt

Error Log

(node:59945) ExperimentalWarning: Conditional exports is an experimental feature. This feature could change at any time
npx: installed 8 in 1.047s
Bundling asset foobar/Foobar/Code/Stage...
WARNING: The directory '/.cache/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
WARNING: The directory '/.cache/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
bash: rsync: command not found
Failed to run bundling Docker image for asset foobar/Foobar/Code/Stage: Error: docker exited with status 127
Subprocess exited with error 1

Environment

• CLI Version : 1.55.0 (build 48ccf09)
• Framework Version: 1.55.0
• Node.js Version: v13.8.0
• OS : Mac OS 19.14.6
• Language (Version): TypeScript (3.9.7) but should be for all

Other

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