CompatHelper: add new compat entry for Downloads at version 1 for package test, (keep existing compat)

[github-actions]

This pull request sets the compat entry for the Downloads package to 1 for package test.
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.
Note: Consider registering a new release of your package immediately after merging this PR, as downstream packages may depend on this for tests to pass.

[ranocha]

ERROR: LoadError: Unsatisfiable requirements detected for package Downloads [f43a241f]:
 Downloads [f43a241f] log:
 ├─possible versions are: 1.5.3 or uninstalled
 └─restricted to versions 1.7.0-1 by an explicit requirement — no versions left

See https://github.com/trixi-framework/Trixi2Vtk.jl/actions/runs/6689393367/job/18172869974?pr=76#step:6:57

Let's wait for an answer in JuliaRegistries/TagBot#292 before deciding how to proceed with this

[sloede]

Do you understand https://github.com/trixi-framework/Trixi2Vtk.jl/actions/runs/7394196279/job/20115204288?pr=76#step:6:45 ?

[ranocha]

CompatHelper PRs automatically enforce running tests with the latest compatible versions of dependencies. In this repo, we use Julia v1.7 for CI. The current version of Trixi.jl requires Julia v1.8.