Error when `run` is used as key

[schneems]

Heroku uses run as a special case. When DYNO=run.1 it indicates that someone is inside of a bash/shell session i.e. heroku run bash. It's currently possible to do this today on the platform, but we should error or at least warn when this collision is present as it may prove difficult to debug why the behavior is different.

Extra Context

$ cat Procfile
run: echo "DYNO: $DYNO"
somethingelse: echo "DYNO: $DYNO"

$ heroku ps:scale run=1
$ heroku logs
2025-08-04T18:36:17.797230+00:00 app[run.1]: DYNO: run.1

$ heroku ps:scale somethingelse=1
$ heroku logs
2025-08-04T18:35:53.190442+00:00 app[somethingelse.1]: DYNO: somethingelse.1