Disable "New" issue button on issue creation view

If the user pressed that button multiple times then the "Dismiss" button
would have to be pressed multiple times too because it just pops the
history.

src/components/IssueSecondColumn.svelte

@@ -8,6 +8,8 @@
   import Icon from "./Icon.svelte";
   import OutlineButton from "./OutlineButton.svelte";
 
+  const activeRouteStore = router.activeRouteStore;
+
   interface Props {
     repo: RepoInfo;
     selectedIssueId?: string;
@@ -36,6 +38,7 @@
 
   <OutlineButton
     variant="ghost"
+    disabled={$activeRouteStore.resource === "repo.createIssue"}
     onclick={() => {
       void router.push({
         resource: "repo.createIssue",