chore(deps): update dependency responses to v0.10.12 (GoogleCloudPlatform#3196)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [responses](https://togithub.com/getsentry/responses) | patch | `==0.10.6` -> `==0.10.12` |

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### Release Notes

<details>
<summary>getsentry/responses</summary>

### [`v0.10.12`](https://togithub.com/getsentry/responses/blob/master/CHANGES#&#8203;01012)

[Compare Source](https://togithub.com/getsentry/responses/compare/0.10.11...0.10.12)

-   Fixed incorrect content-type in `add_callback()` when headers are provided as a list of tuples.

### [`v0.10.11`](https://togithub.com/getsentry/responses/blob/master/CHANGES#&#8203;01011)

[Compare Source](https://togithub.com/getsentry/responses/compare/0.10.9...0.10.11)

-   Fixed invalid README formatted.
-   Fixed string formatting in error message.

### [`v0.10.9`](https://togithub.com/getsentry/responses/blob/master/CHANGES#&#8203;0109)

[Compare Source](https://togithub.com/getsentry/responses/compare/0.10.8...0.10.9)

-   Fixed regression with `add_callback()` and content-type header.
-   Fixed implicit dependency on urllib3>1.23.0

### [`v0.10.8`](https://togithub.com/getsentry/responses/blob/master/CHANGES#&#8203;0108)

[Compare Source](https://togithub.com/getsentry/responses/compare/0.10.7...0.10.8)

-   Fixed cookie parsing and enabled multiple cookies to be set by using a list of
    tuple values.

### [`v0.10.7`](https://togithub.com/getsentry/responses/blob/master/CHANGES#&#8203;0107)

[Compare Source](https://togithub.com/getsentry/responses/compare/0.10.6...0.10.7)

-   Added pypi badges to README.
-   Fixed formatting issues in README.
-   Quoted cookie values are returned correctly now.
-   Improved compatibility for pytest 5
-   Module level method names are no longer generated dynamically improving IDE navigation.

</details>

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testing/requirements.txt

@@ -8,7 +8,7 @@ pytest-cov==2.8.1
 pytest==5.3.2; python_version > "3.0"
 pytest==4.6.9; python_version < "3.0"
 pyyaml==5.3.1
-responses==0.10.6
+responses==0.10.12
 WebTest==2.0.34
 webapp2==2.5.2
 google-api-python-client==1.7.11