Always use is_ci() instead of IS_CI?

[findmyway]

I find that IS_CI is defined as a constant in this package:

Books.jl/src/ci.jl

Lines 1 to 2 in 93376d9

	is_ci() = "CI" in keys(ENV)
	const IS_CI = is_ci()

I'm afraid this is not the standard way to do so.

The IS_CI is defined as a const, which means it will be precompiled and will never be changed later. The direct result is that users can not modify it by setting the CI environment variable to test the local building pipeline.

I'd recommend using is_ci() instead of IS_CI throughout this package.

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I suspect this is the root cause of the incorrect rendering of https://cn.julialang.org/JuliaDataScience/ . (The online_url_prefix is added but it doesn't take into effect)

[rikhuijzer]

I suspect this is the root cause of the incorrect rendering of https://cn.julialang.org/JuliaDataScience/ . (The online_url_prefix is added but it doesn't take into effect)

The issue is actually #241. It's fixed in main, but I didn't tag it yet. I'll tag a new Books version now.

[findmyway]

Thanks!