chore(deps): update dependency google-cloud-bigquery to v2.21.0

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
google-cloud-bigquery	==2.20.0 -> ==2.21.0

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Release Notes

googleapis/python-bigquery

v2.21.0

Compare Source

Features

• Add max_results parameter to some of the QueryJob methods. (#​698) (2a9618f)
• Add support for decimal target types. (#​735) (7d2d3e9)
• Add support for table snapshots. (#​740) (ba86b2a)
• Enable unsetting policy tags on schema fields. (#​703) (18bb443)
• Make it easier to disable best-effort deduplication with streaming inserts. (#​734) (1246da8)
• Support passing struct data to the DB API. (#​718) (38b3ef9)

Bug Fixes

• Inserting non-finite floats with insert_rows(). (#​728) (d047419)
• Use pandas function to check for NaN. (#​750) (67bc5fb)

Documentation

• Add docs for all enums in module. (#​745) (145944f)
• Omit mention of Python 2.7 in CONTRIBUTING.rst. (#​706) (27d6839)

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