Update 17.11.1 release date to 2026-09-29

Updates date.17_11_1 in variables.yml, which feeds the release notes title,
the release notes index, and the mkdocs nav entry.

Signed-off-by: Naeem Akhter <naeem.akhter@percona.com>

Author: Naeem-Akhter

variables.yml

@@ -10,7 +10,7 @@ pgsmversion: '2.4.0'
 
 date:
   17_12_1: TBD
-  17_11_1: 2026-08-19
+  17_11_1: 2026-09-29
   17_10_2: 2026-07-06
   17_10_1: 2026-05-20
   17_9_1: 2026-03-02