Remove jQuery .attr from the branch/tag selector (#30010)

- Switched from jQuery `.attr` to plain javascript `.setAttribute`
- Tested the cherry-pick from the branch/tag selector and it works as
before

Signed-off-by: Yarden Shoham <git@yardenshoham.com>

web_src/js/components/RepoBranchTagSelector.vue

@@ -83,7 +83,7 @@ const sfc = {
  this.isViewBranch = false;
  this.$refs.dropdownRefName.textContent = item.name;
  if (this.setAction) {
- $(`#${this.branchForm}`).attr('action', url);
+ document.getElementById(this.branchForm)?.setAttribute('action', url);
  } else {
  $(`#${this.branchForm} input[name="refURL"]`).val(url);
  }