These religions, due to anti discrimination laws, are given leeway regarding certain things. This includes things like Turbans, the Kirban or a Headscarf (which I will again point out is interpreted from the Hadith and considered a requirement by a pretty large number of Muslims).
The reason Christianity is not given leeway for things like this is because they don't HAVE any requirements which conflict with laws or dress codes which they ACTIVELY FOLLOW (your Sunday working thing is completely irrelevant for this reason) that are even up for interpretation.
The disparity is not between how different religions are treated but between the religions themselves which results in the way they are treated.