Update workflows for nightly tests

[ajschmidt8]

Description

Due to some limitations on the number of reusable workflows that can be used in a given GH Action workflow, I need to switch the nightly workflow files (build.yaml and test.yaml) to use workflow_dispatch instead of workflow_call.

Because of this switch, we can also remove the hardcoded repo field in {build,test}.yaml.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[ajschmidt8]

cc: @bdice, we'll have to make these changes for all of the repos.

I'll start opening PRs for the repos that have already been merged.

Here's a quick sed command that can be run from the root of each project to make the changes programmatically:

sed -i 's/workflow_call/workflow_dispatch/; /repo:/d' ./.github/workflows/{build,test}.yaml

[ajschmidt8]

admin merging since changes are benign and not tested in PRs.