Fix Less test for function-calc-no-invalid

[LolliDepp]

Which issue, if any, is this issue related to?

This changes 2 test cases to highlight the issues explained on #4533

Is there anything in the PR that needs further explanation?

The syntax which was replaced and is now gone I don't think has any value inside of that test file.
It's not related to that rule at all.

The syntax that was being allowed was actually just plain wrong, but not for the reason being reported.
The issue is more along the lines of "You cannot directly do variable interpolations in the value section of CSS properties"

See LESS docs... http://lesscss.org/features/#variables-feature

allowed to interpolate in properties:

@{my-var}: 10px

allowed to interpolate in class names:

.@{my-var} { 
  width: 10px 
}

allowed to interpolate in strings:

background: url("@{base-url}-red.png");

[jeddy3]

@LolliDepp Thank you for fixing the syntax of these tests

The issue is more along the lines of "You cannot directly do variable interpolations in the value section of CSS properties"

Thank you also for breaking down the valid usage of interpolation in Less so clearly.

I proposed a fix in #4533 that should address the now failing tests in this PR.