pgsql: Don't enter parallel mode when holding interrupts.

Don't enter parallel mode when holding interrupts.

Doing so caused the leader to hang in wait_event=ParallelFinish, which
required an immediate shutdown to resolve.  Back-patch to v12 (all
supported versions).

Francesco Degrassi

Discussion: https://postgr.es/m/CAC-SaSzHUKT=vZJ8MPxYdC_URPfax+yoA1hKTcF4ROz_Q6z0_Q@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ac04aa84a7f06635748278e6ff4bd74751bb3e8e

Modified Files
--------------
src/backend/optimizer/plan/planner.c          |  6 ++++++
src/test/regress/expected/select_parallel.out | 24 +++++++++++++++++++++
src/test/regress/sql/select_parallel.sql      | 31 +++++++++++++++++++++++++++
3 files changed, 61 insertions(+)