formula.rb currently overrides `TERM` to "dumb" in the test environment,
which is sensible for non-interactive tests. However, when running in
debug mode and dropping into an interactive shell, leaving `TERM` as
"dumb" breaks terminal capabilities, causing weird behaviour like making
prompt disappear at times. To avoid this, restore the user's original
`TERM` when starting an interactive shell. This also matches the build
environment where we don't override `TERM` to "dumb".

Co-authored-by: Mike McQuaid <mike@mikemcquaid.com>

extend/kernel: restore user `TERM` in interactive shell

…ternal-api

Use installed keg formula files when referencing installed formulae/dependencies

…rmulae/dependencies"

Handle missing `GITHUB_*` variables.

`brew determine-test-runners`: allow running locally.

…l-formulae-internal-api

Revert "Use installed keg formula files when referencing installed formulae/dependencies"