Fix the release cheat sheet - Rekor ID Fetch

Instructions were using gcr instead of ghcr

Author: khrm

tekton/release-cheat-sheet.md

@@ -103,7 +103,7 @@ the triggers repo, a terminal window and a text editor.
 
     ```bash
     RELEASE_FILE=https://storage.googleapis.com/tekton-releases/triggers/previous/${VERSION_TAG}/release.yaml
-    CONTROLLER_IMAGE_SHA=$(curl $RELEASE_FILE | sed -n 's/"//g;s/.*gcr\.io.*controller.*@//p;')
+    CONTROLLER_IMAGE_SHA=$(curl $RELEASE_FILE | sed -n 's/"//g;s/.*ghcr\.io.*controller.*@//p;')
     REKOR_UUID=$(rekor-cli search --sha $CONTROLLER_IMAGE_SHA | grep -v Found | head -1)
     echo -e "CONTROLLER_IMAGE_SHA: ${CONTROLLER_IMAGE_SHA}\nREKOR_UUID: ${REKOR_UUID}"
     ```