chore: fix ci

Author: SelaseKay

packages/cloud_firestore/cloud_firestore/test/pipeline_expression_test.dart

@@ -750,24 +750,24 @@ void main() {
 
     test('timestampAddLiteral serializes correctly', () {
       final ts = Field('created');
-      final expr = Expression.timestampAddLiteral(ts, 'days', 1);
+      final expr = Expression.timestampAddLiteral(ts, 'day', 1);
       expect(expr.toMap(), {
         'name': 'timestamp_add',
         'args': {
           'timestamp': ts.toMap(),
-          'unit': 'days',
+          'unit': 'day',
           'amount': Constant(1).toMap(),
         },
       });
     });
 
     test('timestampTruncate serializes correctly', () {
-      final expr = Expression.timestampTruncate(Field('ts'), 'days');
+      final expr = Expression.timestampTruncate(Field('ts'), 'day');
       expect(expr.toMap(), {
         'name': 'timestamp_truncate',
         'args': {
           'timestamp': Field('ts').toMap(),
-          'unit': 'days',
+          'unit': 'day',
         },
       });
     });