Fixed polyfill for TypeBuilder.CreateType

[lostmsu]

What does this implement/fix? Explain your changes.

The TypeBuilder.CreateType() polyfill was incorrectly returning typeof(TypeBuilder) instead of the new type created using TypeBuilder.

Does this close any currently open issues?

#1228

Checklist

Check all those that are applicable and complete.

• Make sure to include one or more tests for your change
• If an enhancement PR, please create docs and at best an example
• Add yourself to AUTHORS
• Updated the CHANGELOG

[codecov-io]

Codecov Report

Merging #1261 into master will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@## master #1261 +/- ## ======================================= Coverage 86.25% 86.25% ======================================= Files 1 1 Lines 291 291 ======================================= Hits 251 251 Misses 40 40 

Flag	Coverage Δ
#setup_linux	64.94% <ø> (ø)
#setup_windows	72.50% <ø> (ø)

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