TestDlopenThreadSafety panics in CI

[kolyshkin]

When TestDlopenThreadSafety is run from GHA CI 'containers / distro-test' jobs,
it panics on Ubuntu 20.04 and Debain Bullseye (but passes on Ubuntu 22.04).

I tried a few things to make it work (increasing container's pid limit, using newer Go version)
and it did not help.

=== RUN   TestDlopenThreadSafety
runtime/cgo: pthread_create failed: Resource temporarily unavailable
SIGABRT: abort
PC=0x7f35d01c9d61 m=2 sigcode=18446744073709551610

goroutine 0 gp=0xc000002c40 m=2 mp=0xc000042808 [idle]:
runtime: g 0 gp=0xc000002c40: unknown pc 0x7f35d01c9d61
stack: frame={sp:0x7f35896ee7c0, fp:0x0} stack=[0x7f35886ef280,0x7f35896eee80)
0x00007f35896ee6c0:  0x000000000000000b  0x00007f35d03a8623 
....
(another thousands goroutines here)

[kolyshkin]

The workaround, which is part of #459, is merged now, so we can close this.