Set expected value of line-height to expanded generic event list summary (GELS) spacer on IRC layout (#10211)

* Set expected line height to an expanded GELS line on IRC layout, add a test
* Add a test for compact modern/group layout
* Create a new test category on timeline.spec.ts
* Rename the class name as 'spacer'
* Add a test for GELS' spacer on bubble layout
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Signed-off-by: Suguru Hirahara <luixxiul@users.noreply.github.com>
Co-authored-by: Germain <germain@souquet.com>

src/components/views/elements/GenericEventListSummary.tsx

@@ -86,7 +86,7 @@ const GenericEventListSummary: React.FC<IProps> = ({
     if (expanded) {
         body = (
             <React.Fragment>
-                <div className="mx_GenericEventListSummary_line">&nbsp;</div>
+                <div className="mx_GenericEventListSummary_spacer">&nbsp;</div>
                 <ol className="mx_GenericEventListSummary_unstyledList">{children}</ol>
             </React.Fragment>
         );