Carefully remove zn_poly from cygwin github workflows

Author: Matthias Koeppe

.github/workflows/ci-cygwin-standard.yml

@@ -63,7 +63,7 @@ jobs:
     with:
       stage: ii-e
       previous_stages: i-*
-      targets: threejs tachyon pillow jmol m4rie sympy lrcalc lcalc symmetrica cliquer libbraiding planarity rw elliptic_curves combinatorial_designs zn_poly sympow
+      targets: threejs tachyon pillow jmol m4rie sympy lrcalc lcalc symmetrica cliquer libbraiding planarity rw elliptic_curves combinatorial_designs sympow
     needs: [cygwin-stage-i-a, cygwin-stage-i-b]
 
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