Return all runner tags when search is empty

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/finders/autocomplete/acts_as_taggable_on/tags_finder.rb

@@ -22,8 +22,7 @@ module Autocomplete
       end
       def filter_by_name(tags)
-        return tags unless search
-        return tags.none if search.empty?
+        return tags unless search.present?
         if search.length >= Gitlab::SQL::Pattern::MIN_CHARS_FOR_PARTIAL_MATCHING
           tags.named_like(search)

changelogs/unreleased/63656-runner-tags-search-dropdown-is-empty.yml

+---
+title: Fix runner tags search dropdown being empty when there are tags
+merge_request: 29985
+author:
+type: fixed

spec/finders/autocomplete/acts_as_taggable_on/tags_finder_spec.rb

@@ -17,13 +17,13 @@ describe Autocomplete::ActsAsTaggableOn::TagsFinder do
     context 'filter by search' do
       context 'with an empty search term' do
-        it 'returns an empty collection' do
-          ActsAsTaggableOn::Tag.create!(name: 'tag1')
-          ActsAsTaggableOn::Tag.create!(name: 'tag2')
+        it 'returns all tags' do
+          tag1 = ActsAsTaggableOn::Tag.create!(name: 'tag1')
+          tag2 = ActsAsTaggableOn::Tag.create!(name: 'tag2')
           tags = described_class.new(params: { search: '' }).execute
-          expect(tags).to be_empty
+          expect(tags).to match_array [tag1, tag2]
         end
       end