feat(code search): replace fuzzy search with union search for indexer (#6947)

Fuzzy searching for code has been known to be problematic #5264 and in my personal opinion isn't very useful.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6947
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: Shiny Nematoda <snematoda.751k2@aleeas.com>
Co-committed-by: Shiny Nematoda <snematoda.751k2@aleeas.com>

modules/indexer/code/indexer_test.go

@@ -100,8 +100,8 @@ func testIndexer(name string, t *testing.T, indexer internal.Indexer) {
 						Page:     1,
 						PageSize: 10,
 					},
-					Filename:       kw.Filename,
-					IsKeywordFuzzy: true,
+					Filename: kw.Filename,
+					Mode:     SearchModeUnion,
 				})
 				require.NoError(t, err)
 				assert.Len(t, kw.IDs, int(total))