flake: `enterprise/coderd TestManagedAgentLimit`

[ThomasK33]

    coderd_test.go:654: 
        	Error Trace:	/home/runner/work/coder/coder/enterprise/coderd/coderd_test.go:654
        	Error:      	Should be empty, but was [Error getting managed agent count: context canceled]
        	Test:       	TestManagedAgentLimit

coder/coder/actions/runs/16449545996/job/46490812842

[johnstcn]

Seen here: https://github.com/coder/coder/actions/runs/16469776765/job/46555850228