KNOX-3345: Fix intermittent testRefreshGatewayConfig test issue

[hanicz]

KNOX-3345 - GatewayServerTest.testRefreshGatewayConfig fails intermittently

What changes were proposed in this pull request?

• The static field GatewayServer.lastReloadTime leaks state between tests. When testGatewayConfigChangeListener runs first, resets lastReloadTime to null for itself but leaves it set after completion.

How was this patch tested?

Ran unit tests locally

Integration Tests

N/A

UI changes

N/A

[github-actions]

Test Results

22 tests   22 ✅  2s ⏱️
 1 suites   0 💤
 1 files     0 ❌

Results for commit 7858f0e.