Comment out Reverse dependency test of Diffractor (#620)

Author: oxinabox

.github/workflows/IntegrationTest.yml

@@ -18,10 +18,10 @@ jobs:
         #  - {user: dpsanders, repo: ReversePropagation.jl}
           - {user: FluxML, repo: Zygote.jl}
         # Diffractor needs to run on Julia nightly
-        include:
-          - julia-version: nightly
-            os: ubuntu-latest
-            package: {user: JuliaDiff, repo: Diffractor.jl}
+        # include:
+        #  - julia-version: nightly
+        #    os: ubuntu-latest
+        #    package: {user: JuliaDiff, repo: Diffractor.jl}
 
     steps:
       - uses: actions/checkout@v2