chore(deps): update dependency google-api-core to v2.7.3 (GoogleCloudPlatform#7855)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [google-api-core](https://togithub.com/googleapis/python-api-core) | `==2.7.2` -> `==2.7.3` | [![age](https://badges.renovateapi.com/packages/pypi/google-api-core/2.7.3/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/pypi/google-api-core/2.7.3/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/pypi/google-api-core/2.7.3/compatibility-slim/2.7.2)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/pypi/google-api-core/2.7.3/confidence-slim/2.7.2)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes


googleapis/python-api-core

### [`v2.7.3`](https://togithub.com/googleapis/python-api-core/blob/HEAD/CHANGELOG.md#​273-httpsgithubcomgoogleapispython-api-corecomparev272v273-2022-04-29)

[Compare Source](https://togithub.com/googleapis/python-api-core/compare/v2.7.2...v2.7.3)



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composer/cicd_sample/utils/requirements-test.txt

@@ -1,4 +1,4 @@
 pytest==7.0.1
 requests==2.27.1
-google-api-core==2.7.2
+google-api-core==2.7.3
 google-resumable-media==2.3.2

monitoring/opencensus/requirements.txt

@@ -1,5 +1,5 @@
 Flask==2.1.0
-google-api-core==2.7.2
+google-api-core==2.7.3
 google-auth==2.6.2
 googleapis-common-protos==1.56.0
 opencensus==0.9.0

monitoring/prometheus/requirements.txt

@@ -1,5 +1,5 @@
 Flask==2.1.0
-google-api-core==2.7.2
+google-api-core==2.7.3
 google-auth==2.6.2
 googleapis-common-protos==1.56.0
 prometheus-client==0.14.1