fixed save all function failing with JSON in body | issue: (#2130)

[DmytroCrawford]

Description

fix for: #2130

Contribution Checklist:

• The pull request only addresses one issue or adds one feature.
• The pull request does not introduce any breaking changes
• I have added screenshots or gifs to help explain the change if applicable.
• I have read the contribution guidelines.
• Create an issue and link to the pull request.

TLDR:

The "saveMultipleRequests" would fail during a save with JSON in the body. There was a reassignment to a read-only object. I fixed this by making the field mutable and reassigning the body if the type is JSON.

Steps to reproduce/test:

1. Create new collection
2. Create 2 new requests
3. Name them something
4. Add a JSON body to them
5. Click to close and click Save all

Prefix:

On an save all exit with JSON in body, save will fail.

Postfix:

Now postfix, the save all function works perfectly without issue.

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