Dependendies: Update Python requirements (#803)

Align requirements with `aiida-core==2.0` which was just released:

* Drop support for Python 3.6 and 3.7
* Add support for Python 3.10

.github/workflows/cd.yml

@@ -60,7 +60,7 @@ jobs:
 
  strategy:
  matrix:
- python-version: ['3.6', '3.7', '3.8', '3.9']
+ python-version: ['3.8', '3.9', '3.10']
 
  services:
  postgres:

.github/workflows/ci.yml

@@ -38,7 +38,7 @@ jobs:
 
  strategy:
  matrix:
- python-version: ['3.6', '3.7', '3.8', '3.9']
+ python-version: ['3.8', '3.9', '3.10']
 
  services:
  postgres:

pyproject.toml

@@ -14,13 +14,12 @@ classifiers = [
  'Framework :: AiiDA',
  'License :: OSI Approved :: MIT License',
  'Programming Language :: Python',
- 'Programming Language :: Python :: 3.6',
- 'Programming Language :: Python :: 3.7',
  'Programming Language :: Python :: 3.8',
  'Programming Language :: Python :: 3.9',
+ 'Programming Language :: Python :: 3.10',
 ]
 keywords = ['aiida', 'workflows']
-requires-python = '>=3.6'
+requires-python = '>=3.8'
 dependencies = [
  'psycopg2-binary<2.9',
  'aiida_core[atomic_tools]~=1.4,>=1.4.4',