CompatHelper: bump compat for Symbolics to 6, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Symbolics package from 5.30.1 to 5.30.1, 6.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[isaacsas]

@ChrisRackauckas is there a migration guide for what has changed / needs to be updated?

[ChrisRackauckas]

If you're not using maketerm then you're fine. See JuliaSymbolics/Symbolics.jl#1196 as the update. I've pinged @0x0f0f0f for a NEWS.md. I think the only other thing that's relevant is that arguments(expr) no longer auto-sorts, so you have to use sorted_arguments for that. But I don't think that level of detail should effect any of our downstream libraries in anything other than maybe some printing or some latex output.

[isaacsas]

We use arguments it seems in many places. No idea if the ordering was relied on in these uses -- most are by @TorkelE.

This use seems like it might be ordering dependent:

Catalyst.jl/src/registered_functions.jl

Line 143 in 36c10b8

args = arguments(expr)

[isaacsas]

In the Latex recipe I used sorted_arguments when updating recently, so that should be ok on our end.

[ChrisRackauckas]

This use seems like it might be ordering dependent:

That shouldn't be changed. The sorting comes down to whether it should lexicographically sort things that are stored as unsorted, which is commutative operations (add, mul).

[ChrisRackauckas]

Awesome, success.

[isaacsas]

Now for the docs.