bug 1721683: update minidump-stackwalk to 2021.07.21
bug 1721683: update minidump-stackwalk to 2021.07.21

This picks up a fix to minidump-stackwalk such that it looks at the
ThreadNamesList stream for threadnames before looking at the crash
annotations.

lonnen/socorro,lonnen/socorro,lonnen/socorro,lonnen/socorro