chore: ignore Diffractor in dependabot (#933)

Author: gdalle

.github/dependabot.yml

@@ -20,4 +20,7 @@ updates:
       # Group all Julia package updates into a single PR:
       all-julia-packages:
         patterns:
-          - "*"
+          - "*"
+    ignore:
+      - dependency-name: "Diffractor"
+        versions: ["<= 0.2.10"]