fix(vcs): cap the Push dialog's height so a long commit list scrolls inside it (#1491)

With many outgoing commits the Push dialog grew to the full screen height and its
whole body scrolled besides the changed-files tree, because the body was not a flex
container and the commit list's flex had no effect. The single- and multi-repository
Push dialogs now open at most 720px tall with the commit list filling the rest and
scrolling on its own; Dialog gets a maxHeight that applies until the user resizes.

Closes #1485

Co-authored-by: jaw52 <53564781+jaw52@users.noreply.github.com>

src/features/vcs/common.module.css

@@ -111,6 +111,10 @@
   border-radius: var(--radius-small);
 }
 /* Push dialogs: the list fills the body so a resizable window shows more rows. */
+.pushDialog > [data-dialog-body] {
+  display: flex;
+  flex-direction: column;
+}
 .pushTreeWrap {
   flex: 1;
   min-height: 220px;
@@ -127,6 +131,7 @@
 }
 /* Push dialogs: the outgoing commits' changed files below the commits, the diff beside them. */
 .pushChanges {
+  flex: none;
   display: flex;
   flex-direction: column;
   min-height: 0;