Merge pull request #2314 from Alizter/push-kzzoywotyzlm

chore: update nix flake

Author: Alizter

flake.lock

@@ -32,6 +32,11 @@
         };
 
         devShells.default =
+          makeDevShell
+            { coq = pkgs.coq_9_0; }
+            { };
+
+        devShells.coq_8_20 =
           makeDevShell
             { coq = pkgs.coq_8_20; }
             { };