build: Downgrade sphinx-reredirects to an older version again and pin…

[nickvergessen]

… notfound-page dep

Currently prod fails:

ERROR: Could not find a version that satisfies the requirement sphinx-reredirects==1.1.0 (from versions: 0.0.0, 0.0.1, 0.1.1, 0.1.2, 0.1.3, 0.1.4, 0.1.5, 0.1.6)
ERROR: No matching distribution found for sphinx-reredirects==1.1.0
/bin/sh: 1: sphinx-build: not found
make: *** [Makefile:55: html-com] Error 127
cp: cannot stat '/build/documentation/admin_manual/_build/html/com/': No such file or directory
make: sphinx-build: No such file or directory
make: *** [Makefile:61: html-lang-en] Error 127
cp: cannot stat '/build/documentation/user_manual/_build/html/': No such file or directory
make: sphinx-build: No such file or directory
make: *** [Makefile:131: latexpdf] Error 127
cp: cannot stat '/build/documentation/user_manual/_build/latex/Nextcloud_User_Manual.pdf': No such file or directory
stopped: return value was non-zero: 1