remove legacy dependency specifier (see https://pip.pypa.io/en/stable…

…/news/#b1-2024-05-06)

requirements.txt

@@ -1,7 +1,7 @@
 urllib3<1.27,>1.21.1  # avoid caching bug
 requests_cache
 ckanapi>=3.5
-flask>=2.2.5<2.3      # 2.3 messes up pip dependencies
+flask<2.3      # 2.3 messes up pip dependencies
 #git+https://github.com/HXLStandard/libhxl-python.git@dev#egg=libhxl # for development
 libhxl==5.2.1         # for release
 flask-caching