test/staging/sm/extensions/regress-645160.js requires non-standard Error().stack

[linusg]

Should be removed or given the feature flag for https://github.com/tc39/proposal-error-stack-accessor.

[polar51]

"I've checked the file (test/staging/sm/extensions/regress-645160.js) and found where to add the feature flag. I can fix this by adding features: [proposal-error-stack-accessor] to the metadata block. Could you assign this to me?

[linusg]

No, just submit a PR.