FIX: make linkcheck work again using Sphinx v5

pyproject.toml

@@ -26,14 +26,14 @@ dev = [
 doc = [
     "ipympl",
     "myst-nb",
-    "sphinx",
     "sphinx-api-relink",
     "sphinx-book-theme",
     "sphinx-comments",
     "sphinx-copybutton",
     "sphinx-design",
     "sphinx-exercise",
     "sphinx-togglebutton",
+    "sphinx~=5.0", # for sphinx-exercise
     {include-group = "notebooks"},
 ]
 jupyter = [
@@ -177,10 +177,10 @@ allowlist_externals =
     sphinx-build
 commands =
     sphinx-build \
-        --builder=html \
-        --fail-on-warning \
         --keep-going \
-        --show-traceback \
+        -b html \
+        -T \
+        -W \
         docs/ docs/_build/html
 description = Build documentation as website
 passenv = *
@@ -228,8 +228,8 @@ allowlist_externals =
 base = doc
 commands =
     sphinx-build \
-        --builder=linkcheck \
-        --show-traceback \
+        -b linkcheck \
+        -T \
         docs/ docs/_build/linkcheck
 description = Check external links in the documentation (requires internet connection)