Replace PGPROC.isBackgroundWorker with isRegularBackend.
Commit
34486b609 effectively redefined isBackgroundWorker as meaning
"not a regular backend", whereas before it had the narrower
meaning of AmBackgroundWorkerProcess(). For clarity, rename the
field to isRegularBackend and invert its sense.
Discussion: https://postgr.es/m/
1808397.
1735156190@sss.pgh.pa.us