Fix ninja Emscripten build

[mcbarton]

Description

Please include a summary of changes, motivation and context for this PR.

Regardless of what generator is used during the Emscripten build, cmake will try and build GoogleTest using make. Therefore you will get an error for any generator besides make.

Fixes # (issue)

Type of change

Please tick all options which are relevant.

• Bug fix
• New feature
• Requires documentation updates

Testing

Please describe the test(s) that you added and ran to verify your changes.

Checklist

• I have read the contribution guide recently

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.78%. Comparing base (180869d) to head (5f23c32).
⚠️ Report is 53 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #648   +/-   ##
=======================================
  Coverage   78.78%   78.78%           
=======================================
  Files           9        9           
  Lines        3851     3851           
=======================================
  Hits         3034     3034           
  Misses        817      817           

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[Vipul-Cariappa]

LGTM!