[bootstrap-4] [CheckboxesWidget] - <form> cannot appear as a descendant of <form>

[kubajal]

Prerequisites

• I have read the documentation;
• In the case of a bug report, I understand that providing a SSCCE example is tremendously useful to the maintainers.
• Ideally, I'm providing a sample JSFiddle or a shared playground link demonstrating the issue.

Link to the JSFiddle: https://jsfiddle.net/cuq1y8n7/7/ (just copy & paste it locally)

Description

A minimal example of CheckboxesWidget from @rjsf/bootstrap-4 causes the error: <form> cannot appear as a descendant of <form>.

Steps to Reproduce

1. Create the following app:

import Form from "@rjsf/bootstrap-4";
[...]
const custom_schema = {
  type: "object",
  properties: {
    arrayTest: {
    	type: "array",
      items: {
      	type: "string",
        enum: ["1", "2", "3"]
      },
      uniqueItems: true
    }
  }
};
const custom_uiSchema = {
  arrayTest: {
  	"ui:widget": "checkboxes"
  }
[...]
ReactDOM.render(<Form schema={custom_schema} uiSchema={custom_uiSchema}/>, 
             document.getElementById("root"));

2. run the app: npm start

Expected behavior

The checkboxes should be rendered without errors.

Actual behavior

The checkboxes are rendered but the console reads:

index.js:1 Warning: validateDOMNesting(...): <form> cannot appear as a descendant of <form>.
    at form
    at http://localhost:3000/static/js/vendors~main.chunk.js:50226:23
    at div
    at http://localhost:3000/static/js/vendors~main.chunk.js:50825:23
    at CheckboxesWidget (http://localhost:3000/static/js/vendors~main.chunk.js:5438:21)
    at Widget.MergedWidget (http://localhost:3000/static/js/vendors~main.chunk.js:11115:33)
    at ArrayField (http://localhost:3000/static/js/vendors~main.chunk.js:6932:102)
    at div
    at http://localhost:3000/static/js/vendors~main.chunk.js:50825:23
    at FieldTemplate (http://localhost:3000/static/js/vendors~main.chunk.js:5319:17)
    at SchemaField (http://localhost:3000/static/js/vendors~main.chunk.js:8905:102)
    at div
    at http://localhost:3000/static/js/vendors~main.chunk.js:50037:23
    at div
    at http://localhost:3000/static/js/vendors~main.chunk.js:51234:23
    at div
    at http://localhost:3000/static/js/vendors~main.chunk.js:50107:23
    at ObjectFieldTemplate (http://localhost:3000/static/js/vendors~main.chunk.js:5345:31)
    at ObjectField (http://localhost:3000/static/js/vendors~main.chunk.js:8257:102)
    at div
    at http://localhost:3000/static/js/vendors~main.chunk.js:50825:23
    at FieldTemplate (http://localhost:3000/static/js/vendors~main.chunk.js:5319:17)
    at SchemaField (http://localhost:3000/static/js/vendors~main.chunk.js:8905:102)
    at form
    at Form (http://localhost:3000/static/js/vendors~main.chunk.js:6177:102)
    at http://localhost:3000/static/js/vendors~main.chunk.js:12559:23

Version

"@rjsf/bootstrap-4": "^2.5.1",
"@rjsf/core": "^2.5.1",

[heath-freenome]

Fixed in v5 beta via #3145