flake: agent/agentssh: panic on MacOS

[johnstcn]

Seen here: https://github.com/coder/coder/actions/runs/15590571046/job/43908338608?pr=18329

=== FAIL: agent/agentssh  (0.00s)
panic: runtime error: unsafe.Slice: ptr is nil and len is not zero

goroutine 1 [running]:
github.com/shirou/gopsutil/v4/cpu.perCPUTimes(0x140004b2900)
	/Users/runner/work/_temp/go-mod-cache/github.com/shirou/gopsutil/v4@v4.25.3/cpu/cpu_darwin.go:158 +0x4dc
github.com/shirou/gopsutil/v4/cpu.TimesWithContext({0x0?, 0x0?}, 0x1)
	/Users/runner/work/_temp/go-mod-cache/github.com/shirou/gopsutil/v4@v4.25.3/cpu/cpu_darwin.go:70 +0x70
github.com/shirou/gopsutil/v4/cpu.Times(...)
	/Users/runner/work/_temp/go-mod-cache/github.com/shirou/gopsutil/v4@v4.25.3/cpu/cpu_darwin.go:59
github.com/shirou/gopsutil/v4/cpu.init.0()
	/Users/runner/work/_temp/go-mod-cache/github.com/shirou/gopsutil/v4@v4.25.3/cpu/cpu.go:65 +0xf0
FAIL	github.com/coder/coder/v2/agent/agentssh	0.043s

[johnstcn]

Should be fixed by https://github.com/shirou/gopsutil/releases/tag/v4.25.4