Modified 1451.lp to test code to permit keywords as constraint names

[jajhall]

Model supplied by @khantute in #1345 failed to load - since it contains a constraint named "end" - which was interpreted as an LP keyword. However, because it's followed by ":", this is illegal in LP files.

Added code to interpret an LP keyword followed by a colon as a constraint name followed by a colon!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.26%. Comparing base (28a9e28) to head (93ae1b1).
⚠️ Report is 23 commits behind head on latest.

Additional details and impacted files

@@            Coverage Diff             @@
##           latest    #2812      +/-   ##
==========================================
- Coverage   80.32%   80.26%   -0.07%     
==========================================
  Files         348      348              
  Lines       86093    86162      +69     
==========================================
- Hits        69157    69154       -3     
- Misses      16936    17008      +72     

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[jajhall]

To clarify, @khantute, it's the keyword followed by colon that's illegal, not your use of "end" as a constraint name!

[odow]

I wrote a proper LP parser last year. Some of the grammar can be horrific!

https://jump.dev/MathOptInterface.jl/stable/submodules/FileFormats/LP/#Whether-variables-can-have-the-same-name-as-a-keyword