Ensure that copy to clipboard button is visible

Truncates files paths in diff file headers so that, when the path is too
long, it is truncated to prevent the copy to clipboard button from being
hidden.

app/assets/javascripts/diffs/components/diff_file_header.vue

@@ -226,7 +226,7 @@ export default {
       <a
         ref="titleWrapper"
         :v-once="!viewDiffsFileByFile"
-        class="gl-mr-2 gl-text-decoration-none!"
+        class="gl-mr-2 gl-text-decoration-none! gl-text-truncate"
         :href="titleLink"
         @click="handleFileNameClick"
       >

changelogs/unreleased/diff-file-header-clipboard-btn-overflow.yml

+---
+title: Ensure that copy to clipboard button is visible
+merge_request: 46466
+author:
+type: fixed