pgsql: Improve code comment

Improve code comment

The previous wording was potentially confusing about the impact of the
OVERRIDING clause on generated columns.  Reword slightly to avoid
that.

Reported-by: jian he <jian.universality@gmail.com>
Reviewed-by: Dean Rasheed <dean.a.rasheed@gmail.com>
Discussion:
https://www.postgresql.org/message-id/flat/CACJufxFMBe0nPXOQZMLTH4Ry5Gyj4m%2B2Z05mRi9KB4hk8rGt9w%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/fff0d1edf567c412c9d78cb10e9b67ce78b8e0cb

Modified Files
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src/backend/rewrite/rewriteHandler.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)