chore(deps): update dependency grpcio-tools to v1.40.0 (GoogleCloudPlatform#6673)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [grpcio-tools](https://grpc.io) | `==1.39.0` -> `==1.40.0` | [![age](https://badges.renovateapi.com/packages/pypi/grpcio-tools/1.40.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/pypi/grpcio-tools/1.40.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/pypi/grpcio-tools/1.40.0/compatibility-slim/1.39.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/pypi/grpcio-tools/1.40.0/confidence-slim/1.39.0)](https://docs.renovatebot.com/merge-confidence/) |

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endpoints/bookstore-grpc-transcoding/requirements.txt

@@ -1,3 +1,3 @@
-grpcio-tools==1.39.0
+grpcio-tools==1.40.0
 google-auth==2.0.0
 six==1.16.0

endpoints/bookstore-grpc/requirements.txt

@@ -1,3 +1,3 @@
-grpcio-tools==1.39.0
+grpcio-tools==1.40.0
 google-auth==2.0.0
 six==1.16.0

endpoints/getting-started-grpc/requirements.txt

@@ -1 +1 @@
-grpcio-tools==1.39.0
+grpcio-tools==1.40.0