Bump vscode-test from 1.4.1 to 1.5.1 (#3188)

* Bump vscode-test from 1.4.1 to 1.5.1

Bumps [vscode-test](https://github.com/Microsoft/vscode-test) from 1.4.1 to 1.5.1.
- [Release notes](https://github.com/Microsoft/vscode-test/releases)
- [Changelog](https://github.com/microsoft/vscode-test/blob/master/CHANGELOG.md)
- [Commits](microsoft/vscode-test@1.4.1...v1.5.1)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

* Bump CI images

We should considering setting up a matrix so we can purposefully test on
the older versions of these images. However, we at least need to bump
the macOS agent for Node, as this updated dependency requires at least
Node 12. The 10.14 image comes with Node 8, and the 10.15 image comes
with Node 14.

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>
Co-authored-by: Andrew Schwartzmeyer <andrew@schwartzmeyer.com>

Author: dependabot-preview[bot]

.vsts-ci/azure-pipelines-ci.yml

@@ -35,18 +35,18 @@ trigger:
 jobs:
 - job: Windows
   pool:
-    vmImage: 'VS2017-Win2016'
+    vmImage: 'windows-2019'
   steps:
   - template: templates/ci-general.yml
 
 - job: macOS
   pool:
-    vmImage: 'macOS-10.14'
+    vmImage: 'macOS-10.15'
   steps:
   - template: templates/ci-general.yml
 
 - job: Linux
   pool:
-    vmImage: 'Ubuntu-16.04'
+    vmImage: 'Ubuntu-20.04'
   steps:
   - template: templates/ci-general.yml