Fix `changed-in` partial when used with multiple paragraphs (#2006)

When used with a text that includes multiple paragraphs, the partial created invalid HTML by nesting `<p>` elements.
It also changed the rendering by making "Changed in vX.XX:" a separate paragraph, when it is inline with a single paragraph.

To change that we do as with "Required" and add "Changed in vX.XX:" to the text before it is rendered, making it inline with the first paragraph.

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

changelogs/internal/newsfragments/2006.clarification

@@ -0,0 +1 @@
+Fix `changed-in` partial when used with multiple paragraphs.

layouts/partials/changed-in.html

@@ -1,15 +1,11 @@
-{{/*
+{{- /*
     Renders the "Changed in [version]:" blocks for x-changedInMatrixVersion
     annotations for openapi parameters
 
     Takes a single 'changes_dict' parameter, which should be a map of
     version -> details pairs.
 */ -}}
-{{ range $ver, $details := .changes_dict -}}
+{{- range $ver, $details := .changes_dict -}}
-  <p>
+    {{- $details = printf "**Changed in `v%s`:** %s" $ver (default "" $details) -}}
-    <strong>
+    {{- $details | page.RenderString (dict "display" "block") -}}
-      Changed in <code>v{{ $ver }}</code>:
-    </strong>
-    {{ $details | markdownify }}
-  </p>
 {{ end -}}