Update Lowkey Vault version (#234)

Signed-off-by: Esta Nagy <nagyesta@gmail.com>

gradle/libs.versions.toml

@@ -1,6 +1,6 @@
 [versions]
 # Warning: this file is used as build trigger, do not add anything else here!
-lowkeyVault = "2.5.0"
+lowkeyVault = "2.5.6"
 
 [libraries]
 lowkey-vault-app = { module = "com.github.nagyesta.lowkey-vault:lowkey-vault-app", version.ref = "lowkeyVault" }