Fix image width on Text Cards to use max-width (#15653)

Co-authored-by: Natalie Casey <ncasey@faros.ai>

frontend/src/metabase/visualizations/visualizations/Text.css

@@ -151,7 +151,7 @@
 }
 
 :local .text-card-markdown img {
-  width: 100%;
+  max-width: 100%;
   height: auto;
 }