Make extlinks work with older and newer sphinx

docs_sphinx/conf.py

@@ -314,5 +314,11 @@ def __getattr__(cls, name):
 highlight_language = 'python'  # instead of python3 (default for sphinx>=1.4)
 
 # Configure linking to github
-extlinks = {'issue': ('https://github.com/brian-team/brian2/issues/%s',
-                      '# %s')}
+import sphinx
+sphinx_version = tuple(int(x) for x in sphinx.__version__.split('.'))
+if sphinx_version >= (4, 0, 0): 
+    extlinks = {'issue': ('https://github.com/brian-team/brian2/issues/%s',
+                          '# %s')}
+else:
+    extlinks = {'issue': ('https://github.com/brian-team/brian2/issues/%s',
+                          '# ')}

docs_sphinx/introduction/release_notes.rst

@@ -7,7 +7,7 @@ This new minor release only fixes two infrastructure issues that came up with th
 
 Selected bug fixes
 ~~~~~~~~~~~~~~~~~~
-- Re-introduce the reference documentation, that was no longer created on https://brian2.readthedocs.org with the latest release (:issue:`1474`). Thanks to Michalis Pagkalos for making us aware of the issue.
+- Re-introduce the reference documentation that was no longer created on https://brian2.readthedocs.org with the latest release (:issue:`1474`). Thanks to Michalis Pagkalos for making us aware of the issue.
 
 Infrastructure improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~