Update requests-mock requirement from ~=1.8.0 to ~=1.12.1

Updates the requirements on [requests-mock](https://github.com/jamielennox/requests-mock) to permit the latest version.
- [Release notes](https://github.com/jamielennox/requests-mock/releases)
- [Commits](jamielennox/requests-mock@1.8.0...1.12.1)

---
updated-dependencies:
- dependency-name: requests-mock
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -3,4 +3,4 @@ azure-mgmt-hdinsight~=1.5.1
 msrestazure~=0.6.4
 mock~=4.0.2
 requests~=2.24.0
-requests-mock~=1.8.0
+requests-mock~=1.12.1