paperless-ngx: Downgrade gotenberg to 7.5.4

Recent versions of *gotenberg* have problems converting LibreOffice
(and Microsoft Office) documents.  See [issue #442] and [issue #576]
for details.  Downgrading from 7.6.1 to 7.5.4 seems to work around the
problem for now.

[issue #442]: https://github.com/gotenberg/gotenberg/issues/442
[issue #576]: https://github.com/gotenberg/gotenberg/issues/576

paperless-ngx/paperless-ngx.yaml

@@ -325,7 +325,7 @@ spec:
     spec:
       containers:
       - name: gotenberg
-        image: docker.io/gotenberg/gotenberg:7.6
+        image: docker.io/gotenberg/gotenberg:7.5.4
         imagePullPolicy: IfNotPresent
         command:
         - gotenberg