Fix `parse_cache_header` signature change

[serenity4]

Base.parse_cache_headers removed its keyword srcfiles_only in https://github.com/JuliaLang/julia/pull/49866, which makes Revise non-functional in nightly.

There are a bunch of other test failures, and I'm not sure I understand the internals enough to address them, but I could identify least two sources (there are probably more):

• LoadError seems to now (sometimes?) hold a Meta.ParseError value for its .error field, breaking a few tests which expect a String instead. A bunch of related error messages seem to have changed too.
• Source files can't be located for Pkg (the associated (::PkgData).info.files is empty, probably that's because of that), breaking related tests.

Anyway, we can probably merge this fix and worry about other failures on nightly later, such that Revise works again on nightly. Or if anyone wants to address nightly failures in a wider swath, that works for me too.

[Keno]

@timholy can you take a look at this to unbreak revise?

[fatteneder]

This is my bad, I apologize! I really thought I had opened a PR here but apparently I did not ...

[Keno]

Not your fault. There's a structural issue in our process that this wasn't noticed - we'll need to fix that.