package.json: update @vscode/test-electron to 2.3.6

Recent releases include fixes for bugs in vscode downloading,
e.g. permission issue on windows, races.

This update fixes the test failure caused during vscode
download and launch for testing. However, this unsurfaced
problems in the recently added vulncheck support.

* Gopls and vscode use different URI encoding styles.
  'goplsFetchVulncheckResult' looks up the relevant result
  using the go.mod file URI, and this different style
  is problematic in particular on windows (e.g. different
  ways of handling drive casing). Fix this bug by normalizing
  the URIs using vscode URI.fsPath.

* Instead of `exit` event, change to watch `close` event
  when running `gopls vulncheck -mode=convert`. Otherwise
  writeVulns promise resolves before all the stdout/stderr
  outputs arrive.

* gopls vulncheck -mode=convert outputs results in both
  stdout and stderr streams. Perfectly combining the two
  streams and mimicking terminal-like experience is tricky.
  Use separate streams and report seperately.

For #3053

Change-Id: I5ac54683b53fdc2243ae6a74ccc39de30f1a8829
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/544497
TryBot-Result: kokoro <[email protected]>
Reviewed-by: Suzy Mueller <[email protected]>
Commit-Queue: Suzy Mueller <[email protected]>
Run-TryBot: Hyang-Ah Hana Kim <[email protected]>
Commit-Queue: Hyang-Ah Hana Kim <[email protected]>

Author: hyangah