Fix axios key name for custom param serializer

[bjester]

Summary

Description of the change(s) you made

• @bjester mistakenly used serializer instead of serialize for the custom param serializer in axios options when updating it to version 1.x; strangely, it was still being invoked although without effect

The axios docs:

// `paramsSerializer` is an optional config in charge of serializing `params`
  paramsSerializer: {
    encode?: (param: string): string => { /* Do custom ops here and return transformed string */ }, // custom encoder function; sends Key/Values in an iterative fashion
    serialize?: (params: Record<string, any>, options?: ParamsSerializerOptions ), // mimic pre 1.x behavior and send entire params object to a custom serializer func. Allows consumer to control how params are serialized.
    indexes: false // array indexes format (null - no brackets, false (default) - empty brackets, true - brackets with indexes)
  },

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References

https://learningequality.slack.com/archives/C0LK8QS9J/p1670253784157849?thread_ts=1669838492.054009&cid=C0LK8QS9J
Resolves #3865

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[akolson]

LGTM. Thanks @bjester