monkey-patching does not work with addons in yarn workspaces

I suspect it may have something to do with how it is reaching in to discover ember-source files

```
stack: TypeError: Cannot read property '_addon' of undefined
at Class._monkeyPatch_EmberDeprecate (/Users/cthoburn/Github/data/node_modules/ember-cli-deprecation-workflow/index.js:63:39)
at Class.setupPreprocessorRegistry (/Users/cthoburn/Github/data/node_modules/ember-cli-deprecation-workflow/index.js:122:12)
at /Users/cthoburn/Github/data/node_modules/ember-cli-preprocess-registry/preprocessors.js:27:13
at Array.forEach ()
at setupRegistryForEachAddon (/Users/cthoburn/Github/data/node_modules/ember-cli-preprocess-registry/preprocessors.js:25:10)
at Object.module.exports.setupRegistry (/Users/cthoburn/Github/data/node_modules/ember-cli-preprocess-registry/preprocessors.js:46:3)
at Class.init (/Users/cthoburn/Github/data/node_modules/ember-cli/lib/models/addon.js:328:7)
at Class.superWrapper [as init] (/Users/cthoburn/Github/data/node_modules/core-object/lib/assign-properties.js:34:20)
at Class.init (/Users/cthoburn/Github/data/packages/-build-infra/src/addon-build-config-for-data-package.js:21:44)
at Class.superWrapper [as init] (/Users/cthoburn/Github/data/node_modules/core-object/lib/assign-properties.js:34:20)
```