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

Since Sphinx 5.2.0, the generated html search page reports all index
entries that match a query term.  Unfortunately even non-main entries
get a high score, placing them before more important search results
such as document titles and domain object names.

Work around this for documentation published on `cmake.org` by removing
the logic from `searchtools.js` in the generated html documentation.

Issue: #25175

.gitlab/os-linux.yml

@@ -622,3 +622,5 @@
           -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