🔧 Remove Python 3.10 support

Trying to install the package for Python 3.10 fails due to an issue with
PyYAML==5.4.1, see:

yaml/pyyaml#724

As we are currently working on a release for `aiida-core` v1.6.X, which does not
support Python 3.10, we remove support for Python 3.10 here as well.

Author: mbercx

.github/workflows/ci.yml

@@ -38,7 +38,7 @@ jobs:
 
         strategy:
             matrix:
-                python-version: ['3.8', '3.9', '3.10']
+                python-version: ['3.8', '3.9']
 
         services:
             rabbitmq:

pyproject.toml

@@ -17,10 +17,9 @@ classifiers = [
     'Programming Language :: Python',
     'Programming Language :: Python :: 3.8',
     'Programming Language :: Python :: 3.9',
-    'Programming Language :: Python :: 3.10',
 ]
 keywords = ['aiida', 'workflows']
-requires-python = '>=3.8'
+requires-python = '>=3.8,<3.10'
 dependencies = [
     'abipy==0.9.6',
     'aiida-abinit~=0.4.0',