Bump jszip, @microsoft/sp-build-web and @microsoft/sp-webpart-workbench

Bumps [jszip](https://github.com/Stuk/jszip), [@microsoft/sp-build-web](http://aka.ms/spfx) and [@microsoft/sp-webpart-workbench](http://aka.ms/spfx). These dependencies needed to be updated together.

Updates `jszip` from 2.5.0 to 3.7.1
- [Release notes](https://github.com/Stuk/jszip/releases)
- [Changelog](https://github.com/Stuk/jszip/blob/main/CHANGES.md)
- [Commits](https://github.com/Stuk/jszip/compare/v2.5.0...v3.7.1)

Updates `@microsoft/sp-build-web` from 1.7.0 to 1.15.2

Updates `@microsoft/sp-webpart-workbench` from 1.7.0 to 1.12.1

---
updated-dependencies:
- dependency-name: jszip
  dependency-type: indirect
- dependency-name: "@microsoft/sp-build-web"
  dependency-type: direct:development
- dependency-name: "@microsoft/sp-webpart-workbench"
  dependency-type: direct:development
...

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

samples/knockout-sp-pnp-js/package.json

@@ -25,10 +25,10 @@
     "knockout": "3.5.0"
   },
   "devDependencies": {
-    "@microsoft/sp-build-web": "1.7.0",
+    "@microsoft/sp-build-web": "1.15.2",
     "@microsoft/sp-tslint-rules": "1.7.0",
     "@microsoft/sp-module-interfaces": "1.7.0",
-    "@microsoft/sp-webpart-workbench": "1.7.0",
+    "@microsoft/sp-webpart-workbench": "1.12.1",
     "gulp": "~3.9.1",
     "@types/chai": "3.4.34",
     "@types/mocha": "2.2.38",