PMM-14515 Bump PT. (#4174)

* trigger

* PMM-14515 PT update.

---------

Co-authored-by: Vasyl Yurkovych <[email protected]>

Author: JiriCtvrtka

.gitmodules

@@ -36,7 +36,7 @@
 [submodule "percona-toolkit"]
 	path = sources/percona-toolkit/src/github.com/percona/percona-toolkit
 	url = https://github.com/percona/percona-toolkit
-	branch = NEEDED-FOR-PMM-3.5
+	branch = release-v3.7.1
 
 # PMM Server
 [submodule "grafana-dashboards"]