[MRG] docs: update google_calendar.py

[eltociear]

What has been done to verify that this works as intended?

calender -> calendar

Why is this the best possible solution? Were any other approaches considered?

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

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Does this change require updates to documentation? If so, please file an issue here and include the link below.

Before submitting this PR, please make sure you have:

• confirmed all checks still pass OR confirm CI build passes.
• verified that any code or assets from external sources are properly credited in comments and/or in
  the credit file.

[leeeizhang]

LGTM! Many thanks for helping us fix the typos! :)