Add JsonSerializable type to phpDoc of $body parameter in makeRequest method

[jankonas]

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

I have not added any documentation because I don't think it's necessary for this change. Also I haven't added any tests, because this type of issues can only be detected by static analysis on files using this package.

Short description of what this PR does:

This PR updates phpDoc comment to reflect the code (not only array, but also JsonSerializable can be passed to makeRequest method). That allows usage of this package in projects using static analysis without the need of suppressing some error messages.

[SendGridDX]

All committers have signed the CLA.

[thinkingserious]

Thank you @jankonas!

This has been added to our backlog for review.

With Best Regards,

Elmer

[thinkingserious]

Hello @jankonas,

Thanks again for the PR!

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