[Release] Update version to 9.1.11 (#48328)

* [Release] update version

* No longer can reference previous SNAPSHOT version - pinning to release

---------

Co-authored-by: elasticmachine <infra-root+elasticmachine@elastic.co>
Co-authored-by: Pierre HILBERT <pierre.hilbert@elastic.co>
Co-authored-by: Eric Beahan <eric.beahan@elastic.co>

Author: 4 people

.buildkite/scripts/custom_fips_ech_test.sh

@@ -12,7 +12,7 @@ trap 'ech_down' EXIT
 # haven't been published yet and are, therefore, not yet available in ECH.
 # Once artifacts matching the version in `libbeat/version/version.go` are available in ECH, the
 # following line should be removed and the line after that should be uncommented.
-STACK_VERSION="9.1.7-SNAPSHOT"
+STACK_VERSION="9.1.10"
 #STACK_VERSION="$(./dev-tools/get_version)-SNAPSHOT"
 
 ech_up $STACK_VERSION