adjust test

Tests/RediStackIntegrationTests/Commands/StringCommandsTests.swift

@@ -232,7 +232,7 @@ final class StringCommandsTests: RediStackIntegrationTestCase {
   
     func test_strlen() throws {
         XCTAssertNoThrow(try connection.set(#function, to: "value").wait())
-        let val = try connection.strlen(#function).wait()
+        let val = try connection.send(.strln(#function)).wait()
         XCTAssertEqual(val, 5)
     }
 }