They means the same and I think we say 週末も仕事でした / 今日は仕事です / 明日は仕事です very often in colloquial. For example, about 今日は仕事です, the literal translation is "today is work" but it means "I have work today / today is the day for work". I hope you understand this.

@JuliaLim Thank you. @Ryoko What is the difference between 仕事をしました and 仕事でした ??

Julia's answer is correct. I'd lime to explain a bit more. I would say: "I worked this weekend." = 今週末、私は仕事をしました。"I worked on Saturday and Sunday (of this week)." = (今週の)土曜日も日曜日も仕事をしました / 仕事でした。