RM-37337: Do not report prefer-const-variables-over-non-const-global-variables on mutations

[brouwers-tiobe]

See RM-37337.

The const annotation should only be checked for a varibale declaration, not mutation. Going by https://docs.julialang.org/en/v1/manual/variables/#man-assignment-expressions, it gives examples of instances of mutation vs assignment:

That is, a[i] = value (an alias for setindex!) mutates an existing array object in memory, accessible via either a or b. Subsequently setting a = 3.14159 does not change this array, it simply binds a to a different object; the array is still accessible via b. Another common syntax to mutate an existing object is a.field = value (an alias for setproperty!), which can be used to change a mutable struct. There is also mutation via dot assignment, for example b .= 5:7 (which mutates our array b in-place to contain [5,6,7]), as part of Julia's vectorized "dot" syntax.

This PR excludes struct mutation and array mutation from prefer-const-variables-over-non-const-global-variables, meaning assignments such as A.x = 1 and A[i] = 2 now are no longer reported on.

[zon-tiobe]

One minor nitpick about annotations is all.

Looks to be good!

[zon-tiobe]

LGTM!