HTTP 502 which happens during Vault login in "KUBERNETES" auth mode is cached indefinitely

Describe the bug

1. Spring boot 4.0.5 + Spring cloud vault 5.0.0 (+spring-vault-core 4.0.0) deployed k8s infra
2. Service uses "KUBERNETES" vault authentication mode
3. Service uses Vault transit to generate JWT signatures (but this is irrelevant actually)
4. Service caches Vault token
5. Vault goes down and all requests to it ends up with 502/504
6. Vault token in Spring service expires
7. Spring cloud vault tries to renew the token using logic org.springframework.vault.authentication.ReactiveLifecycleAwareSessionManager#scheduleRenewal
8. As Vault is unavailable org.springframework.vault.authentication.ReactiveLifecycleAwareSessionManager#doRenewToken catches the exception and cleans the mono cache: org.springframework.vault.authentication.ReactiveLifecycleAwareSessionManager#token
9. Following getVaultToken() calls (scheduled, or triggered by user interactions) infect Mono cache with a Mono which returns 502/504 and is cached indefinitely: org/springframework/vault/authentication/ReactiveLifecycleAwareSessionManager.java:330

Sample

VaultSessionCachingBugIntegrationTest.java

Start with org/springframework/vault/authentication/ReactiveLifecycleAwareSessionManager.java, especially the token cache around line 330 and the renewal flow in scheduleRenewal and doRenewToken. Use the linked VaultSessionCachingBugIntegrationTest.java as the reproduction; done means a transient 502/504 during Vault recovery is not cached indefinitely and token acquisition works after Vault returns.