Add desc to Suggests to fix R CMD check warning

The test-description_helpers.R uses desc::desc() which triggers
'import not declared' warning, treated as error by rworkflows.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bschilder

DESCRIPTION

@@ -44,8 +44,9 @@ Imports:
     parallel,
     rworkflows
 Suggests:
+    desc,
     markdown,
-    rmarkdown, 
+    rmarkdown,
     testthat (>= 3.0.0),
     remotes,
     knitr,