Minor cleanup to use constants

[enamkhan]

Would like to use constants where possible so this is just a bit of minor cleanup.

Review Checklist
I certify that I have:

• tested my changes
• added/updated automated tests
• updated the changelog
• followed the contribution guidelines

Additional Comments

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 40.80%. Comparing base (2d13589) to head (7e145a2).

Files with missing lines	Patch %	Lines
...ees/CICSCombinedTrees/CICSCombinedLocalFileTree.ts	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #240      +/-   ##
==========================================
+ Coverage   40.78%   40.80%   +0.02%     
==========================================
  Files         151      151              
  Lines        5056     5058       +2     
  Branches      817      860      +43     
==========================================
+ Hits         2062     2064       +2     
  Misses       2994     2994              

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[AndrewTwydell]

Nice thanks, good catch