runtime: `fatal: systemstack called from unexpected goroutine` testing runtime/trace on freebsd-386-12_3

[bcmills]

freebsd-386-12_3 at 4afb0b9e533767f788252816c4b79ee29a1952a7
…
fatal: systemstack called from unexpected goroutine
FAIL	runtime/trace	7.741s

(CC @golang/freebsd)

This may or may not be related to #51001 (CC @golang/runtime, @prattmic, @aclements):

greplogs -l -e 'fatal: systemstack called from unexpected goroutine\nFAIL\s+runtime'
2022-06-08T15:47:58-4afb0b9/freebsd-386-12_3
2022-05-20T22:30:37-2b0e457/android-arm64-corellium
2022-05-03T19:48:07-bccce90/android-arm64-corellium

[prattmic]

Minor note: the android results above are in package runtime, so they are already included in #51001. As Bryan mentions, the runtime/trace may or may not be related, it is unclear with so little data.