doc: Fix title markup for AT TIME ZONE and AT LOCAL

doc: Fix title markup for AT TIME ZONE and AT LOCAL

The title for AT TIME ZONE and AT LOCAL was accidentally wrapping the
"and" in the <literal> tag.  Backpatch to v17 where it was introduced
in 97957fdbaa42.

Author: Noboru Saito <[email protected]>
Reviewed-by: Daniel Gustafsson <[email protected]>
Reviewed-by: Tatsuo Ishii <[email protected]>
Reviewed-by: Michael Paquier <[email protected]>
Discussion: https://postgr.es/m/CAAM3qn+7QUWW9R6_YwPKXmky0xGE4n63U3EsxZeWE_QtogeU8g@mail.gmail.com
Backpatch-through: 17