embedded-book failures don't block beta

Author: mark-i-m

src/ci/docker/x86_64-gnu-tools/checkregression.py

@@ -5,7 +5,7 @@
 import json
 
 # Regressions for these tools do not cause failure.
-REGRESSION_OK = ["rustc-guide", "miri"]
+REGRESSION_OK = ["rustc-guide", "miri", "embedded-book"]
 
 if __name__ == '__main__':
     os_name = sys.argv[1]