TST: update mock download parameterization

[aburrell]

Description

Update the mock download parameterization to use the appropriate key after pysat issue pysat/pysat#1158 is implemented.

Potential impact

• Is the feature related to an existing problem? Cannot fully test TestMockDownloads on CI
• How critical is this feature to your workflow? Necessary
• How wide of an impact to you anticipate this enhancement having? Allow potential errors to be caught
• Would this break any existing functionality? No

Potential solution(s)

Update test suite once a new pysat key is available

Alternatives

Find a way to re-create the inst_dict locally.

Additional context

See: #133