[CI] fix failing CI integrations

[art-divin]

Context

Step validate_docs in Rakefile fails consistently, and only sometimes locally.

The reason is the following error when running sourcekitten doc --spm --module-name SourceryRuntime > docs.json command:

 [1/1] Compiling plugin SourceryCommandPlugin
 Building for debugging...
 error: command /Users/art-divin/Documents/Projects/Sourcery/.build/arm64-apple-macosx/debug/Sourcery_SourceryJS.bundle/ejs.js not registered
 [1/12] Copying ejs.js
 [1/12] Compiling scanner.c
 ...

Seems like for some reason, swift compiler fails to compile from within sourcekitten tool, but I was only able to reproduce it locally 2 out of dozens of times running this command differently - directly or via rake.

At the moment, it is best to disable this verification, because unit tests are not being executed and thus regressions could be introduced.