CLS fix for gist examples

i think there are a few blocks that can appear above the fold eg. here:
https://main--helix-website--adobe.hlx3.page/docs/indexing-reference

i think it would be great to remove the CLS impacts for those blocks, i am not sure what the best strategy, for the gists it could be that a the height might be fixed.

Start by inspecting the blocks that appear above the fold on docs/indexing-reference, especially the gist examples linked in the issue. Measure their layout shift and identify a strategy that prevents the blocks from changing size; done means those examples no longer contribute avoidable CLS.

Written by the indexing model from the issue text.