[bug] Fix test case failure

[FZambia]

Describe the bug. A clear and concise description of what the bug is.

Happened occasionally in CI:

=== RUN   TestHandleRefreshWithoutProxyServerStart
    refresh_handler_test.go:198: 
        	Error Trace:	/home/runner/work/centrifugo/centrifugo/internal/proxy/refresh_handler_test.go:198
        	Error:      	Not equal: 
        	            	expected: centrifuge.RefreshReply{Expired:false, ExpireAt:1730532433, Info:[]uint8(nil)}
        	            	actual  : centrifuge.RefreshReply{Expired:false, ExpireAt:1730532434, Info:[]uint8(nil)}
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -2,3 +2,3 @@
        	            	  Expired: (bool) false,
        	            	- ExpireAt: (int64) 1730532433,
        	            	+ ExpireAt: (int64) 1730532434,
        	            	  Info: ([]uint8) <nil>
        	Test:       	TestHandleRefreshWithoutProxyServerStart
        	Messages:   	http
--- FAIL: TestHandleRefreshWithoutProxyServerStart (0.03s)