User lenient decoder for infra status

[kon-angelo]

How to categorize this PR?

/area control-plane
/kind bug
/platform azure

What this PR does / why we need it:
Due to the removal of the natGatewayPublicIpMigrated field in #406 currently existing shoots may have their reconciliation blocked if they try to reconcile worker resources (e.g. scaling a worker pool) without first reconciling the Infrastructure.

The issue occurs due to the extra field in existing infrastructureStatus that is not allowed from the strict decoder. This PR uses a non-strict decoder to decode the infrastructureStatus.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Release note:

Azure provider extension now uses non-strict decoder for InfrastructrureStatus resources.

[gardener-robot]

@kon-angelo Labels area/todo, kind/todo do not exist.

[kon-angelo]

/test

[testmachinery]

Testrun: e2e-8bvq4
Workflow: e2e-8bvq4-wf
Phase: Succeeded

+---------------------+---------------------+-----------+----------+
|        NAME         |        STEP         |   PHASE   | DURATION |
+---------------------+---------------------+-----------+----------+
| infrastructure-test | infrastructure-test | Succeeded | 25m25s   |
+---------------------+---------------------+-----------+----------+

[dkistner]

/lgtm