Fix incorrect tailwind migration (#30007)

Fixes https://github.com/go-gitea/gitea/issues/30005. Regression from
https://github.com/go-gitea/gitea/pull/29945.

There was only once instance of `tw-content-center` before that PR, so I
just ran below command and reverted that one instance.

```sh
perl -p -i -e 's#tw-content-center#tw-items-center#g' web_src/js/**/* templates/**/* models/**/* tests/**/*
```

web_src/js/components/RepoRecentCommits.vue

@@ -121,7 +121,7 @@ export default {
 </script>
 <template>
   <div>
-    <div class="ui header tw-flex tw-content-center tw-justify-between">
+    <div class="ui header tw-flex tw-items-center tw-justify-between">
       {{ isLoading ? locale.loadingTitle : errorText ? locale.loadingTitleFailed: "Number of commits in the past year" }}
     </div>
     <div class="tw-flex ui segment main-graph">