flake: TestLogin/InitialUserTTY: copy did not close in time

[johnstcn]

Seen here: https://github.com/coder/coder/actions/runs/20332463742/job/58410869393

    ptytest.go:101: 2025-12-18 09:39:32.290: cmd: close: copy did not close in time
    ptytest.go:101: 
        	Error Trace:	/home/runner/work/coder/coder/pty/ptytest/ptytest.go:374
        	            				/home/runner/work/coder/coder/pty/ptytest/ptytest.go:101
        	            				/home/runner/work/coder/coder/pty/ptytest/ptytest.go:391
        	            				/opt/hostedtoolcache/go/1.24.10/x64/src/sync/once.go:78
        	            				/opt/hostedtoolcache/go/1.24.10/x64/src/sync/once.go:69
        	            				/home/runner/work/coder/coder/pty/ptytest/ptytest.go:386
        	            				/home/runner/work/coder/coder/pty/ptytest/ptytest.go:40
        	            				/opt/hostedtoolcache/go/1.24.10/x64/src/testing/testing.go:1211
        	            				/opt/hostedtoolcache/go/1.24.10/x64/src/testing/testing.go:1445
        	            				/opt/hostedtoolcache/go/1.24.10/x64/src/testing/testing.go:1786
        	Error:      	close
        	Test:       	TestLogin/InitialUserTTY
        	Messages:   	copy did not close in time