build(deps-dev): bump @microsoft/sp-webpart-workbench

Bumps [@microsoft/sp-webpart-workbench](http://aka.ms/spfx) from 1.10.0 to 1.12.1.

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

Author: dependabot[bot]

package.json

@@ -35,7 +35,7 @@
     "@microsoft/sp-build-web": "1.10.0",
     "@microsoft/sp-tslint-rules": "1.10.0",
     "@microsoft/sp-module-interfaces": "1.10.0",
-    "@microsoft/sp-webpart-workbench": "1.10.0",
+    "@microsoft/sp-webpart-workbench": "1.12.1",
     "@microsoft/rush-stack-compiler-3.3": "0.3.5",
     "gulp": "~3.9.1",
     "@types/chai": "3.4.34",