Bump rsa from 4.6 to 4.7 in /src/emailservice (GoogleCloudPlatform#537)

Bumps [rsa](https://github.com/sybrenstuvel/python-rsa) from 4.6 to 4.7.
- [Release notes](https://github.com/sybrenstuvel/python-rsa/releases)
- [Changelog](https://github.com/sybrenstuvel/python-rsa/blob/main/CHANGELOG.md)
- [Commits](sybrenstuvel/python-rsa@version-4.6...version-4.7)

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src/emailservice/requirements.txt

@@ -94,7 +94,7 @@ requests==2.24.0
     #   -r requirements.in
     #   google-api-core
     #   google-cloud-profiler
-rsa==4.6
+rsa==4.7
     # via google-auth
 six==1.15.0
     # via