Add a comment explaining an edge-case.

Author: chrisgavin

lib/codeql.js

@@ -97,6 +97,8 @@ function getCodeQLActionRepository(): string {
   const runnerTemp = util.getRequiredEnvParam("RUNNER_TEMP");
   const actionsDirectory = path.join(path.dirname(runnerTemp), "_actions");
   const relativeScriptPath = path.relative(actionsDirectory, __filename);
+  // This handles the case where the Action does not come from an Action repository,
+  // e.g. our integration tests which use the Action code from the current checkout.
   if (relativeScriptPath.startsWith("..") || path.isAbsolute(relativeScriptPath)) {
     return CODEQL_DEFAULT_ACTION_REPOSITORY;
   }