Correct embedded documentation typos in kernelSpecs.json

[Copilot]

This PR addresses a single review comment on PR #3687 requesting exact typo fixes in user-facing embedded documentation strings. The change is limited to the suggested wording updates in kernelSpecs.json.

• Scope

  • Updated only documentation text under doc.combinations.vars and doc.explicit.
  • No functional/configuration logic changes.

• Applied review suggestion (exact wording fixes)

  • combinatorally → combinatorially
  • concating → concatenating
  • can by modified → can be modified

• Patch excerpt

  "vars" : [ "each value in this list will be used to generate kernel template files",
             "combinatorially with all other value lists" ],
  "explicit" : [ "specify a specific combination of the variables to generate",
                 "specify by choosing one value from each variable you want generated",
                 "and concatenating them with '#' (this can be modified internally at the",
                 "generation call). Duplicate entries are unified internally" ]