CompatHelper: bump compat for GR to 0.66 for package docs, (keep existing compat) (#1588)

Co-authored-by: CompatHelper Julia <[email protected]>

Author: github-actions[bot]

docs/Project.toml

@@ -4,4 +4,4 @@ GR = "28b8d3ca-fb5f-59d9-8090-bfdbd6d07a71"
 
 [compat]
 Documenter = "0.26, 0.27"
-GR = "0.61, 0.62, 0.63, 0.64, 0.65"
+GR = "0.61, 0.62, 0.63, 0.64, 0.65, 0.66"