Make the signtool usage in windows-packaging less brittle

[mstoykov]

          This looks really brittle :thinking:

Originally posted by @olegbespalov in #4102 (comment)

The current way to sign windows executables uses signtool which is part of windows kit. Unfortuantely it isn't in the path by default and the path to the exact location is dependant on the version of the windows kit.

k6/.github/workflows/build.yml

Lines 246 to 247 in ba6a71e

	- name: Add signtool to PATH
	run: echo "${env:ProgramFiles(x86)}\Windows Kits\10\bin\10.0.17763.0\x64" | Out-File -FilePath $env:GITHUB_PATH -Append

Moving from windows-2019 to windows-2022 github action image meant that the path chagned and we had to fix it.

Given the information I found there doesn't seem to be a fix for this. If we ran from the terminal inside visual studio that sets the path correctly ... which doesn't seem like a good thing for a CI ;).

Luckily there aren't that many windows releases so hopefully we need to fix this once every 3-4 years, but it will still be nice if it isn't as brittle as it is.