fix(actiongroup): revert flex: 1 setting for vertical-justified

- for justified action groups, specify that the desired effect is for
them to grow to fill the available space (as opposed to allow allowing
flex-shrink)
- add changeset

Author: marissahuysentruyt

.changeset/calm-ears-think.md

@@ -0,0 +1,7 @@
+---
+"@spectrum-css/actiongroup": patch
+---
+
+Action group
+
+`flex: 1` has now changed to `flex-grow: 1` in the `.spectrum-ActionGroup--justified .spectrum-ActionGroup-item` selector to specify the desired behavior of justified action groups.

components/actiongroup/index.css

@@ -154,5 +154,5 @@
 }
 
 .spectrum-ActionGroup--justified .spectrum-ActionGroup-item {
-	flex: 1;
+	flex-grow: 1;
 }