Fix s3 put_object example

[tim-finnigan]

Fixes boto/boto3#4126

The example is on this page: https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/s3/client/put_object.html

This PR fixes the example and makes it consistent with other examples here and here.

---

Although this fixes an inconsistency, the examples are still misleading as mentioned in boto/boto3#4126 (comment).

Do we want to update each of them to be like this?

with open('HappyFace.jpg', 'rb') as file:
    response = client.put_object(
        Body=file.read(),
        Bucket='examplebucket',
        Key='HappyFace.jpg',
    )

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.14%. Comparing base (8fd0160) to head (f470ce5).
Report is 280 commits behind head on develop.

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Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3177   +/-   ##
========================================
  Coverage    93.14%   93.14%           
========================================
  Files           66       66           
  Lines        14237    14248   +11     
========================================
+ Hits         13261    13272   +11     
  Misses         976      976           

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[SamRemis]

Yes, I'd like to see these examples be reworked if we have the bandwidth- would you be okay making those changes and updating this PR @tim-finnigan ?