Bump keystoneauth1 from 5.5.0 to 5.6.0 (#1727)

Bumps [keystoneauth1](https://docs.openstack.org/keystoneauth/latest/) from 5.5.0 to 5.6.0.

---
updated-dependencies:
- dependency-name: keystoneauth1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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requirements_swift.txt

@@ -1,3 +1,3 @@
-keystoneauth1==5.5.0
+keystoneauth1==5.6.0
 openstackclient==4.0.0
 python-swiftclient==4.5.0