build(deps): re-pin single-kernel to 4a6ab71 (reachable stack tip)

The previously-pinned lib commit was orphaned when the TLS stack was rebalanced
(the tests moved to their own PR, renaming the tip branch). Re-pin to the new
reachable stack tip; the packaged library source is byte-identical.

Signed-off-by: Marcelo Henrique Neppel <marcelo.neppel@canonical.com>

Author: marceloneppel

poetry.lock

@@ -23,7 +23,7 @@ charmlibs-systemd = "^1.0.0.post0"
 charmlibs-interfaces-tls-certificates = "^1.8.3"
 
 [tool.poetry.group.single-kernel.dependencies]
-postgresql-charms-single-kernel = {url = "https://github.com/canonical/postgresql-single-kernel-library/archive/f4480ca.zip", extras = ["postgresql"]}
+postgresql-charms-single-kernel = {url = "https://github.com/canonical/postgresql-single-kernel-library/archive/4a6ab71.zip", extras = ["postgresql"]}
 
 [tool.poetry.group.charm-libs.dependencies]
 # data_platform_libs/v0/data_interfaces.py