chore(deps): update dependency google-cloud-dialogflow to v2.5.0 (#326)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [google-cloud-dialogflow](https://togithub.com/googleapis/dialogflow-python-client-v2) | `==2.4.0` -> `==2.5.0` | [![age](https://badges.renovateapi.com/packages/pypi/google-cloud-dialogflow/2.5.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/pypi/google-cloud-dialogflow/2.5.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/pypi/google-cloud-dialogflow/2.5.0/compatibility-slim/2.4.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/pypi/google-cloud-dialogflow/2.5.0/confidence-slim/2.4.0)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>googleapis/dialogflow-python-client-v2</summary>

### [`v2.5.0`](https://togithub.com/googleapis/dialogflow-python-client-v2/blob/master/CHANGELOG.md#&#8203;250-httpswwwgithubcomgoogleapispython-dialogflowcomparev240v250-2021-06-26)

[Compare Source](https://togithub.com/googleapis/dialogflow-python-client-v2/compare/v2.4.0...v2.5.0)

##### Features

-   added Automated agent reply type and allow cancellation flag for partial response feature ([#&#8203;314](https://www.github.com/googleapis/python-dialogflow/issues/314)) ([5dfd375](https://www.github.com/googleapis/python-dialogflow/commit/5dfd375c389e41e8d87055a6479cfb9c0b5f2e37))
-   **v2beta1:** added Automated agent reply type and allow cancellation flag for partial response feature ([#&#8203;311](https://www.github.com/googleapis/python-dialogflow/issues/311)) ([1d34763](https://www.github.com/googleapis/python-dialogflow/commit/1d34763b13902162f567fac7768d08619f77f81e))

##### Documentation

-   added notes to train agent prior to sending queries ([#&#8203;319](https://www.github.com/googleapis/python-dialogflow/issues/319)) ([37dece2](https://www.github.com/googleapis/python-dialogflow/commit/37dece29c4f2b852f5d5426fb10c6c8b55d9bff6))
-   omit mention of Python 2.7 in 'CONTRIBUTING.rst' ([#&#8203;1127](https://www.github.com/googleapis/python-dialogflow/issues/1127)) ([#&#8203;316](https://www.github.com/googleapis/python-dialogflow/issues/316)) ([55fcb9d](https://www.github.com/googleapis/python-dialogflow/commit/55fcb9d366a27318e7f044f15984df8f3fb32f8e))
-   update comment in ListSuggestions to use absolute URL for /apis/design/design_patterns ([#&#8203;313](https://www.github.com/googleapis/python-dialogflow/issues/313)) ([99d8897](https://www.github.com/googleapis/python-dialogflow/commit/99d8897a9a576bcf1d3887c5d40ec86efd8e3ec4))

</details>

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dialogflow/requirements.txt

@@ -1 +1 @@
-google-cloud-dialogflow==2.4.0
+google-cloud-dialogflow==2.5.0