[checklocks]: source file and line number sometimes not printed

Description

sometimes I see:

-: return with unexpected locks held (locks: &({param:f}.mu) exclusively)

notice the usual file name and line number is replaced by -.

Steps to reproduce

go: downloading gvisor.dev/gvisor v0.0.0-20241120231458-0add1d20fa0c

I haven't been able to extract a simple repro (the fact that I can't tell where the error is happening makes it harder). I happen to believe these are false positive as well but it's hard to prove without knowing what it's unhappy about :-)

runsc version

docker version (if using docker)

uname

No response

kubectl (if using Kubernetes)

repo state (if built from source)

No response

runsc debug logs (if available)