installation: pin Flask to <2.3.0

Author: slint

setup.cfg

@@ -27,7 +27,8 @@ python_requires = >=3.7
 zip_safe = False
 install_requires =
     blinker>=1.4
-    Flask>=1.1.4,<3.0.0
+    # Pinned because of https://github.com/inveniosoftware/invenio-base/issues/171
+    Flask>=1.1.4,<2.3.0
     itsdangerous>=1.1.0,<2.1.0
     MarkupSafe>=0.23
     Werkzeug>=1.0.1,<3.0