haikumodern: main auto rows should be min-content.

Otherwise on pages where the content is less than a full page, the
spacing gets messy. Using min-content acts similar to normal block
flow, fixing the issue.

theme/haikumodern/static/haikumodern.css.jinja

@@ -221,8 +221,8 @@ main {
 	overflow-x: clip;
 
 	display: grid;
-	grid-template-rows: 1fr;
 	grid-template-columns: subgrid;
+	grid-auto-rows: min-content;
 	margin: 0;
 	padding-left: 1em;
 	padding-right: 1em;