Update codeql-analysis.yml

Author: songyumeng

.github/workflows/codeql-analysis.yml

@@ -4,6 +4,8 @@
 # You may wish to alter this file to override the set of languages analyzed,
 # or to provide custom queries or build logic.
 name: "CodeQL"
+env:
+  LGTM_INDEX_EXCLUDE: src
 on:
   push:
     branches: [master]