doc: fix spelling "connction" to "connection"

Bruce Momjian <bruce@momjian.us>

Commit: 1393acb3836d32e512801bb00f0cc6b4d2a58dc8
Author: Bruce Momjian <bruce@momjian.us>
Date: 2020-11-11T00:18:35Z
Releases: 12.6
doc: fix spelling "connction" to "connection"

Was wrong in commit 1a9388bd0f.

Reported-by: Tom Lane, Justin Pryzby

Discussion: https://postgr.es/m/20201102063333.GE22691@telsasoft.com

Backpatch-through: 9.5

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Documentation touched