release-19.sgml: "This this" should be "This"

[zengman]

Hi,

doc/src/sgml/release-19.sgml: 
https://github.com/postgres/postgres/blob/41ddb9c33eadc7fec0745b86943c87f3a465cd40/doc/src/sgml/release-19.sgml#L247

Current:
  "This this change requires sites..."

Should be:
  "This change requires sites..."

("This" is duplicated.)

Regards,
Man Zeng