The content-length header only gets updated at request object
initialization, so make sure we update it here after we modified the
body.

Fixes #1403

Co-authored-by: Anthonios Partheniou <partheniou@google.com>

## Deleted keys were detected in the following pre-stable discovery artifacts:
analyticsadmin v1alpha 3ed7887

## Discovery Artifact Change Summary:
feat(analyticsadmin): update the api 3ed7887
feat(composer): update the api 4862529
feat(genomics): update the api 8a1c8a6
feat(gkehub): update the api 0fd49e0

## Deleted keys were detected in the following stable discovery artifacts:
managedidentities v1 e96adbb

## Discovery Artifact Change Summary:
feat(appengine): update the api ffcf860
feat(containeranalysis): update the api 9a1c70b
feat(documentai): update the api 07a6e77
feat(drive): update the api 773910f
feat(managedidentities): update the api e96adbb
feat(spanner): update the api 87da2f3

## Deleted keys were detected in the following pre-stable discovery artifacts:
analyticsadmin v1alpha a715d2b

## Discovery Artifact Change Summary:
feat(analyticsadmin): update the api a715d2b
feat(apigee): update the api 9fcf80b
feat(chat): update the api 47ff8a5

## Deleted keys were detected in the following pre-stable discovery artifacts:
managedidentities v1alpha1 0927c19
managedidentities v1beta1 0927c19

## Discovery Artifact Change Summary:
feat(managedidentities): update the api 0927c19

🤖 I have created a release \*beep\* \*boop\*
---
## [2.9.0](https://www.github.com/googleapis/google-api-python-client/compare/v2.8.0...v2.9.0) (2021-06-12)


### Features

* **analyticsadmin:** update the api 3ed7887 ([33237a8](https://www.github.com/googleapis/google-api-python-client/commit/33237a8250e3becfaa1e4b5f67ef0c887cfc44a9))
* **analyticsadmin:** update the api a715d2b ([0f0918f](https://www.github.com/googleapis/google-api-python-client/commit/0f0918f92a699753b52c77dd236ad84ee00a32a7))
* **apigee:** update the api 9fcf80b ([0f0918f](https://www.github.com/googleapis/google-api-python-client/commit/0f0918f92a699753b52c77dd236ad84ee00a32a7))
* **appengine:** update the api ffcf860 ([26aa9e2](https://www.github.com/googleapis/google-api-python-client/commit/26aa9e282e30ca9c8797ee5346cbe9c0b9ca65a7))
* **chat:** update the api 47ff8a5 ([0f0918f](https://www.github.com/googleapis/google-api-python-client/commit/0f0918f92a699753b52c77dd236ad84ee00a32a7))
* **composer:** update the api 4862529 ([33237a8](https://www.github.com/googleapis/google-api-python-client/commit/33237a8250e3becfaa1e4b5f67ef0c887cfc44a9))
* **containeranalysis:** update the api 9a1c70b ([26aa9e2](https://www.github.com/googleapis/google-api-python-client/commit/26aa9e282e30ca9c8797ee5346cbe9c0b9ca65a7))
* **documentai:** update the api 07a6e77 ([26aa9e2](https://www.github.com/googleapis/google-api-python-client/commit/26aa9e282e30ca9c8797ee5346cbe9c0b9ca65a7))
* **drive:** update the api 773910f ([26aa9e2](https://www.github.com/googleapis/google-api-python-client/commit/26aa9e282e30ca9c8797ee5346cbe9c0b9ca65a7))
* **genomics:** update the api 8a1c8a6 ([33237a8](https://www.github.com/googleapis/google-api-python-client/commit/33237a8250e3becfaa1e4b5f67ef0c887cfc44a9))
* **gkehub:** update the api 0fd49e0 ([33237a8](https://www.github.com/googleapis/google-api-python-client/commit/33237a8250e3becfaa1e4b5f67ef0c887cfc44a9))
* **managedidentities:** update the api 0927c19 ([c3f8675](https://www.github.com/googleapis/google-api-python-client/commit/c3f86757bccb6b42552f87d37a645651c58d6c7a))
* **managedidentities:** update the api e96adbb ([26aa9e2](https://www.github.com/googleapis/google-api-python-client/commit/26aa9e282e30ca9c8797ee5346cbe9c0b9ca65a7))
* **spanner:** update the api 87da2f3 ([26aa9e2](https://www.github.com/googleapis/google-api-python-client/commit/26aa9e282e30ca9c8797ee5346cbe9c0b9ca65a7))


### Bug Fixes

* update content-length header for next page ([#1404](https://www.github.com/googleapis/google-api-python-client/issues/1404)) ([8019f2f](https://www.github.com/googleapis/google-api-python-client/commit/8019f2f96abc6a4375873becb2f17b399f738654)), closes [#1403](https://www.github.com/googleapis/google-api-python-client/issues/1403)
---


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