Fix spacing for branch switcher in pipeline editor

This makes sure that the top and bottom margins are the same
and removes the left margin to align the branch switcher with
the rest of the page.

Changelog: changed

app/assets/javascripts/pipeline_editor/components/file_nav/branch_switcher.vue

@@ -146,7 +146,6 @@ export default {
 <template>
   <gl-dropdown
     v-if="showBranchSwitcher"
-    class="gl-ml-2"
     :header-text="$options.i18n.dropdownHeader"
     :text="currentBranch"
     icon="branch"

app/assets/javascripts/pipeline_editor/components/file_nav/pipeline_editor_file_nav.vue

@@ -15,7 +15,7 @@ export default {
 };
 </script>
 <template>
-  <div class="gl-mb-5">
+  <div class="gl-mb-4">
     <branch-switcher v-if="showBranchSwitcher" v-on="$listeners" />
   </div>
 </template>