Change SOAPpy version for erp5-zope2.

The version used for SOAPpy in erp5-zope2 was 0.12.0nxd001.
This is not a PEP 440-compliant version and thus compilation with the
newer buildout fails with:

``
Getting distribution for 'SOAPpy==0.12.0nxd001'.
DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support pip 21.0 will remove support for this functionality.
  WARNING: Built wheel for SOAPpy is invalid: Metadata 1.2 mandates PEP 440 version, but '0.12.0nxd001' is not
ERROR: Failed to build one or more wheels
```

We upgrade the version to 0.12.22, which is the same that was done for
erp5 SR when buildout was upgraded.

stack/erp5-zope2/buildout.cfg

@@ -743,8 +743,8 @@ PasteDeploy = 1.5.2
 argparse = 1.4.0
 zope.dottedname = 4.1.0
 
-# modified version that works fine for buildout installation
-SOAPpy = 0.12.0nxd001
+# version that works fine for buildout installation
+SOAPpy = 0.12.22
 
 # CMF 2.3 is not yet supported.
 Products.CMFCalendar = 2.2.3