Fix: autoprefix giving a warning about align-content (#2178)

* Fix: autoprefix giving a warning about align-content

* Create good-colts-jam.md

Author: jonrohan

.changeset/good-colts-jam.md

@@ -0,0 +1,5 @@
+---
+"@primer/css": patch
+---
+
+Fix: autoprefix giving a warning about align-content

src/layout/stack.scss

@@ -35,7 +35,7 @@
   display: flex;
   flex-flow: column;
   align-items: stretch;
-  align-content: start;
+  align-content: flex-start;
   gap: var(--Stack-gap-whenRegular);
 
   @media ($viewport-narrow) {