pgsql: Improve documentation example for jsonpath like_regex operator

Improve documentation example for jsonpath like_regex operator

Make sample like_regex match string values of the root object instead of the
whole document.  The corrected example seems to represent a more relevant
use case.

Backpatch to 12, when jsonpath was introduced.

Discussion: https://postgr.es/m/13440f8b-4c1f-5875-c8e3-f3f65606af2f%40xs4all.nl
Author: Erik Rijkers
Reviewed-by: Michael Paquier, Alexander Korotkov
Backpatch-through: 12

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/ff91d3a22b9a5ab9511f8ed8bffc895a991529f5

Modified Files
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doc/src/sgml/func.sgml | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)