CompatHelper: bump compat for StructArrays to 0.7, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the StructArrays package from 0.6.18 to 0.6.18, 0.7.
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.

[graeme-a-stewart]

An upgrade isn't currently possible because of Accessors:

(JetReconstruction) pkg> add StructArrays@0.7
   Resolving package versions...
ERROR: Unsatisfiable requirements detected for package StructArrays [09ab397b]:
 StructArrays [09ab397b] log:
 ├─possible versions are: 0.0.1 - 0.7.0 or uninstalled
 ├─restricted to versions 0.6.18 - 0.7 by JetReconstruction [44e8cb2c], leaving only versions: 0.6.18 - 0.7.0
 │ └─JetReconstruction [44e8cb2c] log:
 │   ├─possible versions are: 0.4.3 or uninstalled
 │   └─JetReconstruction [44e8cb2c] is fixed to version 0.4.3
 ├─restricted to versions 0.7 by an explicit requirement, leaving only versions: 0.7.0
 └─restricted by compatibility requirements with Accessors [7d9f7c33] to versions: 0.6.0 - 0.6.21 or uninstalled — no versions left
   └─Accessors [7d9f7c33] log:
     ├─possible versions are: 0.1.0 - 0.1.38 or uninstalled
     └─restricted to versions 0.1.36 - 0.1 by JetReconstruction [44e8cb2c], leaving only versions: 0.1.36 - 0.1.38
       └─JetReconstruction [44e8cb2c] log: see above

[Moelf]

JuliaObjects/Accessors.jl#178

I have nudged them to upgrade

[graeme-a-stewart]

Tested now against the Accessors master branch and it's all good.