ci,cdash: fix GITHUB_SHA var

Author: vicentebolea

.github/post-cdash-status

@@ -26,7 +26,7 @@ command -v curl &> /dev/null || { echo "jq not found"; exit 1; }
 command -v jq &> /dev/null || { echo "jq not found"; exit 2; }
 
 [ -z "${CI_GITHUB_ROBOT_TOKEN}" ] && { echo "CI_GITHUB_ROBOT_TOKEN env variable empty"; exit 3; }
-[ -z "${COMMIT_SHA}" ] && { echo "COMMIT_SHA env variable empty"; exit 4; }
+[ -z "${GITHUB_SHA}" ] && { echo "GITHUB_SHA env variable empty"; exit 4; }
 
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