Fix continuous integration (#47)

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
-          python-version: 3.8
+          python-version: "3.9"
       - name: Install python dependencies
         env:
           INSTALL_TYPE: docs
@@ -45,7 +45,9 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
-          python-version: 3.8
+          # Using the oldest supported Python version here, to ensure
+          # compatible type stubs will be installed.
+          python-version: "3.7"
       - name: Install python dependencies
         env:
           INSTALL_TYPE: dev_precommit
@@ -58,10 +60,10 @@ jobs:
     timeout-minutes: 20
     strategy:
       matrix:
-        python-version: [3.7, 3.8]
+        python-version: ["3.7", "3.8", "3.9"]
         install-type: [testing]
         include:
-          - python-version: 3.8
+          - python-version: "3.9"
             install-type: testing_sdist
     services:
       postgres:

.pre-commit-config.yaml

@@ -1,6 +1,6 @@
 repos:
 
-- repo: git://github.com/pre-commit/mirrors-yapf
+- repo: https://github.com/pre-commit/mirrors-yapf
   rev: v0.30.0
   hooks:
   - id: yapf

setup.json

@@ -14,6 +14,7 @@
     "License :: OSI Approved :: Apache Software License",
     "Programming Language :: Python :: 3.7",
     "Programming Language :: Python :: 3.8",
+    "Programming Language :: Python :: 3.9",
     "Topic :: Scientific/Engineering :: Physics",
     "Framework :: AiiDA"
   ],
@@ -39,7 +40,8 @@
     "docs": [
       "sphinx",
       "sphinx-rtd-theme",
-      "sphinxcontrib-details-directive"
+      "sphinxcontrib-details-directive",
+      "markupsafe==2.0.1"
     ],
     "testing": [
       "pytest~=6.0",