Making scala-steward able to update deps for unlinked *Sample projects

[blast-hardcheese]

I read through scala-steward in order to figure out why library upgrades for sample subprojects weren't getting opened.

It turns out it's because the stewardDependencies task walks libraryDependencies for root and aggregated tasks.

Unfortunately, as *Sample projects are not designed to be aggregated (they don't pass compile unless we're running testSuite), it necessitated some hoop jumping.

A more long-term solution would be to modify scala-steward to be able to run the stewardPlugin against non-root projects, but as this is a fairly niche use case, I'm OK with this solution for now.

Contributing to Twilio

All third-party contributors acknowledge that any contributions they provide will be made under the same open-source license that the open-source project is provided under.

• I acknowledge that all my contributions will be made under the project's license.

[codecov-commenter]

Codecov Report

Merging #664 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #664   +/-   ##
=======================================
  Coverage   81.13%   81.13%           
=======================================
  Files          78       78           
  Lines        5163     5163           
  Branches      130      130           
=======================================
  Hits         4189     4189           
  Misses        974      974           

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