Update python-gnupg requirement from >=0.4.7 to >=0.5.6

Updates the requirements on [python-gnupg](https://github.com/vsajip/python-gnupg) to permit the latest version.
- [Release notes](https://github.com/vsajip/python-gnupg/releases)
- [Changelog](https://github.com/vsajip/python-gnupg/blob/master/release)
- [Commits](vsajip/python-gnupg@0.4.7...0.5.6)

---
updated-dependencies:
- dependency-name: python-gnupg
  dependency-version: 0.5.6
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements/base.txt

@@ -35,7 +35,7 @@ pymssql==2.3.11; sys_platform == 'win32'
 pymysql>=1.0.2; sys_platform == 'win32'
 pyopenssl>=26.0.0
 python-dateutil>=2.8.1
-python-gnupg>=0.4.7
+python-gnupg>=0.5.6
 pythonnet>=3.0.1; sys_platform == 'win32'
 pywin32>=305; sys_platform == 'win32'
 pycryptodomex>=3.9.8