Fix typo in Javadoc snippet of AsyncRequestBody.forBlockingOutputStream

[KENNYSOFT]

Motivation and Context

I found a typo and would like to correct it. Fixes #6141

Modifications

Correct return type of AsyncRequestBody.forBlockingOutputStream

Testing

N/A

Screenshots (if appropriate)

N/A

However, I encountered a local test failure due to the throwable message i18n, which seems to be from the OS:

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)

Checklist

• [x] I have read the CONTRIBUTING document
• [ ] Local run of mvn install succeeds
• [x] My code follows the code style of this project
• [x] My change requires a change to the Javadoc documentation
• [x] I have updated the Javadoc documentation accordingly
• [ ] I have added tests to cover my changes
• [ ] All new and existing tests passed
• [x] I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.
• [ ] My change is to implement 1.11 parity feature and I have updated LaunchChangelog

License

• [x] I confirm that this pull request can be released under the Apache 2 license