use correct description string for dotnet build -h: -c

[FLGMwt]

Changed dotnet build -h output to use the correct string for the --configuration flag (it was erroneously using the same as --framework.

fixes #5506

[dnfclas]

Hi @FLGMwt, I'm your friendly neighborhood .NET Foundation Pull Request Bot (You can call me DNFBOT). Thanks for your contribution!

This seems like a small (but important) contribution, so no Contribution License Agreement is required at this point. Real humans will now evaluate your PR.

TTYL, DNFBOT;

[dnfclas]

@FLGMwt, Thanks for signing the contribution license agreement so quickly! Actual humans will now validate the agreement and then evaluate the PR.

Thanks, DNFBOT;