Set max-height for description container

Without max-height, the description text can overflow the image, making
it impossible to close.

See issue #199: AkkomaGang/pleroma-fe#199

src/components/attachment/attachment.scss

@@ -26,6 +26,7 @@
     display: flex;
     padding-top: 0.5em;
     z-index: 1;
+    max-height: 50%;
 
     p {
       flex: 1;