Allow filtering issues by any assignee (#33343)

This is the opposite of the "No assignee" filter, it will match all
issues that have at least one assignee.

Before
![Before
change](https://github.com/user-attachments/assets/4aea194b-9add-4a84-8d6b-61bfd8d9e58e)

After
![After change with any
filter](https://github.com/user-attachments/assets/99f1205d-ba9f-4a0a-a60b-cc1a0c0823fe)

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/indexer/issues/indexer_test.go

@@ -44,6 +44,7 @@ func TestDBSearchIssues(t *testing.T) {
 	t.Run("search issues with order", searchIssueWithOrder)
 	t.Run("search issues in project", searchIssueInProject)
 	t.Run("search issues with paginator", searchIssueWithPaginator)
+	t.Run("search issues with any assignee", searchIssueWithAnyAssignee)
 }
 
 func searchIssueWithKeyword(t *testing.T) {
@@ -176,19 +177,19 @@ func searchIssueByID(t *testing.T) {
 	}{
 		{
 			opts: SearchOptions{
-				PosterID: optional.Some(int64(1)),
+				PosterID: "1",
 			},
 			expectedIDs: []int64{11, 6, 3, 2, 1},
 		},
 		{
 			opts: SearchOptions{
-				AssigneeID: optional.Some(int64(1)),
+				AssigneeID: "1",
 			},
 			expectedIDs: []int64{6, 1},
 		},
 		{
-			// NOTE: This tests no assignees filtering and also ToSearchOptions() to ensure it will set AssigneeID to 0 when it is passed as -1.
-			opts:        *ToSearchOptions("", &issues.IssuesOptions{AssigneeID: optional.Some(db.NoConditionID)}),
+			// NOTE: This tests no assignees filtering and also ToSearchOptions() to ensure it handles the filter correctly
+			opts:        *ToSearchOptions("", &issues.IssuesOptions{AssigneeID: "(none)"}),
 			expectedIDs: []int64{22, 21, 16, 15, 14, 13, 12, 11, 20, 5, 19, 18, 10, 7, 4, 9, 8, 3, 2},
 		},
 		{
@@ -462,3 +463,25 @@ func searchIssueWithPaginator(t *testing.T) {
 		assert.Equal(t, test.expectedTotal, total)
 	}
 }
+
+func searchIssueWithAnyAssignee(t *testing.T) {
+	tests := []struct {
+		opts          SearchOptions
+		expectedIDs   []int64
+		expectedTotal int64
+	}{
+		{
+			SearchOptions{
+				AssigneeID: "(any)",
+			},
+			[]int64{17, 6, 1},
+			3,
+		},
+	}
+	for _, test := range tests {
+		issueIDs, total, err := SearchIssues(t.Context(), &test.opts)
+		require.NoError(t, err)
+		assert.Equal(t, test.expectedIDs, issueIDs)
+		assert.Equal(t, test.expectedTotal, total)
+	}
+}