Doc: Update the reference link of fastapi

[hungtsetse]

The reference of fastapi doc has been changed. Update the path accrodingly.

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update
• [ ] Refactor
• [x] Other, please describe: Documentation

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

If yes, please describe the impact and migration path for existing applications:

(If no, please delete the above question and this text message.)

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[lepture]

Thanks