CI: change dependabot prefix to "CI" (#13724)

The default prefix of dependabot is "build(deps)".  Change it to "CI".

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 5ace460..5487348 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -4,3 +4,5 @@
     directory: "/"
     schedule:
       interval: "weekly"
+    commit-message:
+      prefix: "CI"