Suppress [WRN] -code flag not found messages during -validate

[princechaddha]

When running nuclei -validate, the CLI outputs multiple [WRN] -code flag not found, skipping code template from workflow warnings for every codetemplate. These warnings are really not required in validation mode since templates aren’t actually executed.

Expected behavior:

• Validation should check template syntax without emitting irrelevant warnings.
• The [WRN] messages should only appear when running templates with missing flags, not during validation.

This would make -validate output cleaner and easier to use for template authors.

[dogancanbakir]

Tracked at #6498