ci: Restore cmake.org html documentation search results for index entries

Sphinx 7.3 fixes the problem motivating commit fbed0431c2 (ci: Suppress
cmake.org html documentation search results for index entries,
2023-08-09, v3.27.2~2^2).  Revert the workaround.

Fixes: #25175

.gitlab/os-linux.yml

@@ -712,5 +712,3 @@
           -DCMake_SPHINX_CMAKE_ORG_OUTDATED=$CMAKE_CI_SPHINX_OUTDATED
           -DCMake_VERSION_NO_GIT=$CMAKE_CI_VERSION_NO_GIT
         - ninja
-        # FIXME(#25175): non-main index entries are scored too high.
-        - sed -i '/search for explicit entries in index directives/,/^$/d' html/_static/searchtools.js