Bugfix: CMAKE_SOURCE_DIR -> PROJECT_SOURCE_DIR

[stigrj]

${CMAKE_SOURCE_DIR}/VERSION picks up the host version file in a super build

[MinazoBot]

	1 Warning
⚠️	There are code changes, but no corresponding tests. Please include tests if this PR introduces any modifications in behavior.

Generated by 🚫 Danger

[codecov]

Codecov Report

Merging #123 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #123   +/-   ##
=======================================
  Coverage   72.15%   72.15%           
=======================================
  Files         139      139           
  Lines        5966     5966           
=======================================
  Hits         4305     4305           
  Misses       1661     1661

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