Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
- [ ] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/python-bigquery/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
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Follow-up to #448

Towards #366

Disable renovate PRs on the .pre-commit-config.yaml which is templated from synthtool. https://docs.renovatebot.com/configuration-options/#ignorepaths

Source-Author: Bu Sun Kim <8822365+busunkim96@users.noreply.github.com>
Source-Date: Mon Mar 15 09:05:39 2021 -0600
Source-Repo: googleapis/synthtool
Source-Sha: 2c54c473779ea731128cea61a3a6c975a08a5378
Source-Link: googleapis/synthtool@2c54c47

#551)

* fix: DB API pyarrow dependency with decimal values

DB API should gracefully handle the case when the optional pyarrow
dependency is not installed.

* Blacken DB API helpers tests

* Refine the logic for recognizing NUMERIC Decimals

🤖 I have created a release \*beep\* \*boop\*
---
## [2.12.0](https://www.github.com/googleapis/python-bigquery/compare/v2.11.0...v2.12.0) (2021-03-16)


### Features

* make QueryJob.done() method more performant ([#544](https://www.github.com/googleapis/python-bigquery/issues/544)) ([a3ab9ef](https://www.github.com/googleapis/python-bigquery/commit/a3ab9efdd0758829845cfcb6ca0ac1f03ab44f64))


### Bug Fixes

* remove DB-API dependency on pyarrow with decimal query parameters ([#551](https://www.github.com/googleapis/python-bigquery/issues/551)) ([1b946ba](https://www.github.com/googleapis/python-bigquery/commit/1b946ba23ee7df86114c6acb338ec34e6c92af6d))
---


This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please).

* WIP: fix: don't set policy tags in load job from dataframe

* copy fields parameter for struct support

* update tests to allow missing description property

* fix load from dataframe test on python 3.6

Also, check that sent schema matches DataFrame order, not table order

Exclude "bignumeric_type" from the "all" extra

…nal sources (#560)

* feat: add `ExternalConfig.connection_id` property to connect to external sources

* add tests

* fix unit tests

)

This change should be non-destructive.

Note for library repo maintainers:
After applying this change, you can easily add (or change) periodic
builds against head by adding config files in google3.

See python-pubsub repo for example.

Source-Author: Takashi Matsuo <tmatsuo@google.com>
Source-Date: Fri Mar 19 11:17:59 2021 -0700
Source-Repo: googleapis/synthtool
Source-Sha: 79c8dd7ee768292f933012d3a69a5b4676404cda
Source-Link: googleapis/synthtool@79c8dd7

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>