CI Check default doctest directives in linter (scikit-learn#17269)

* add grep

* directs to test CI

* attempt2

* better output format

* use find

* revert test rst file

* better message

* faster grep

build_tools/circle/linting.sh

@@ -161,3 +161,14 @@ then
     echo $bad_deprecation_property_order
     exit 1
 fi
+
+# Check for default doctest directives ELLIPSIS and NORMALIZE_WHITESPACE
+
+doctest_directive="$(git grep -nw -E "# doctest\: \+(ELLIPSIS|NORMALIZE_WHITESPACE)")"
+
+if [ ! -z "$doctest_directive" ]
+then
+    echo "ELLIPSIS and NORMALIZE_WHITESPACE doctest directives are enabled by default, but were found in:"
+    echo "$doctest_directive"
+    exit 1
+fi