chore: disable cosign testing for now

[btlghrants]

Description

Had a chat w/ Sam, Kim today -- the cosign/sigstore-js tests are subject to intermittent failure in CI due to a (suspected) failed network request (which presents as an "invalid bundle"-ish error message). Changing nothing & simply rerunning the CI job is usually enough to "fix it", but... that's not the kind of thing we want to have to constantly be doing.

So, while we will have to dig into that more in the future -- probably once the cosign signature verification helper graduates from "spike" status -- we're just going to disable running these tests in CI for the time being. Not only will this prevent us having to see a bunch of false-fails (until we get time to go back & make this feature "real") but it should also (slightly) increase the perf of our test suite by not running tests that aren't required.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (security config, docs update, etc)

Checklist before merging

• Unit, Journey, E2E Tests, docs, adr added or updated as needed
• Contributor Guide Steps followed

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.57%. Comparing base (9dbf9ab) to head (8f96c07).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1368      +/-   ##
==========================================
- Coverage   79.69%   79.57%   -0.13%     
==========================================
  Files          40       39       -1     
  Lines        1945     1816     -129     
  Branches      411      396      -15     
==========================================
- Hits         1550     1445     -105     
+ Misses        365      342      -23     
+ Partials       30       29       -1     

see 1 file with indirect coverage changes