[CODEOWNERS] Add EngSys to /dev/, /.vscode/, and /specification/suppressions.yaml (#35155)

Author: mikeharder

.github/CODEOWNERS

@@ -296,9 +296,12 @@
 /tsconfig.json      @weshaggard @mikeharder
 /.azure-pipelines/  @weshaggard @mikeharder @benbp
 /.github/           @weshaggard @mikeharder @benbp
+/.vscode/           @weshaggard @mikeharder @benbp
+/dev/               @weshaggard @mikeharder @benbp
 /eng/               @weshaggard @mikeharder @benbp
 /eng/common/        @Azure/azure-sdk-eng
 /eng/tools/typespec-migration-validation @pshao25 @live1206
 /eng/tools/typespec-validation/src/rules/sdk-tspconfig-validation.ts @wanlwanl @raych1 @maririos
 /scripts/           @weshaggard @mikeharder
+/specification/suppressions.yaml @weshaggard @mikeharder @benbp @raych1
 /.github/CODEOWNERS @Azure/azure-sdk-eng