Update apache/skywalking-eyes digest to 21648e7

Author: renovate[bot]

.github/workflows/license-check.yaml

@@ -9,4 +9,4 @@ jobs:
     steps:
     - uses: actions/checkout@master
     - name: Check License Header
-      uses: apache/skywalking-eyes/header@61275cc80d0798a405cb070f7d3a8aaf7cf2c2c1
+      uses: apache/skywalking-eyes/header@21648e752a1dad42cb46b50b38e77f0a8f15219c