pgsql: Don't consider parallel append for parallel unsafe paths.

Don't consider parallel append for parallel unsafe paths.

Commit ab72716778 allowed Parallel Append paths to be generated for a
relation that is not parallel safe.  Prevent that from happening.

Initial analysis by Tom Lane.

Reported-by: Rajkumar Raghuwanshi
Author: Amit Kapila and Rajkumar Raghuwanshi
Reviewed-by: Amit Khandekar and Robert Haas
Discussion:https://postgr.es/m/CAKcux6=tPJ6nJ08r__nU_pmLQiC0xY15Fn0HvG1Cprsjdd9s_Q@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/403318b71f7058ecbfb65bcc7de1eec96cd35d3f

Modified Files
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src/backend/optimizer/path/allpaths.c         |  5 ++++-
src/test/regress/expected/select_parallel.out | 26 ++++++++++++++++++++++++++
src/test/regress/sql/select_parallel.sql      |  9 +++++++++
3 files changed, 39 insertions(+), 1 deletion(-)