Move more CI to 20.09 (attempt 2)

ci.nix

@@ -24,14 +24,12 @@
     # Update supported-ghc-versions.md to reflect any changes made here.
     {
       ghc865 = true;
-    } // nixpkgs.lib.optionalAttrs (nixpkgsName == "R2003") {
+    } // nixpkgs.lib.optionalAttrs (nixpkgsName == "R2009") {
       ghc883 = false;
       ghc884 = true;
       ghc8101 = false;
       ghc8102 = true;
       ghc810220201118 = false;
-    } // nixpkgs.lib.optionalAttrs (nixpkgsName == "R2009") {
-      ghc8102 = true;
     });
   systems = nixpkgs: nixpkgs.lib.filterAttrs (_: v: builtins.elem v supportedSystems) {
     # I wanted to take these from 'lib.systems.examples', but apparently there isn't one for linux!
@@ -42,9 +40,11 @@
     # We need to use the actual nixpkgs version we're working with here, since the values
     # of 'lib.systems.examples' are not understood between all versions
     let lib = nixpkgs.lib;
-    in lib.optionalAttrs (nixpkgsName == "R2003" && (__elem compiler-nix-name ["ghc865" "ghc884"])) {
+    in lib.optionalAttrs (nixpkgsName == "R2009" && (__elem compiler-nix-name ["ghc865" "ghc884"])) {
     inherit (lib.systems.examples) ghcjs;
-  } // lib.optionalAttrs (system == "x86_64-linux" && (nixpkgsName == "R2009" || (!(__elem compiler-nix-name ["ghc8101" "ghc8102" "ghc810220201118"])))) {
+  } // lib.optionalAttrs (system == "x86_64-linux" && (
+         (nixpkgsName == "R2009" && __elem compiler-nix-name ["ghc8101" "ghc8102" "ghc810220201118"])
+      || (nixpkgsName == "R2003" && __elem compiler-nix-name ["ghc865"]))) {
     # Windows cross compilation is currently broken on macOS
     inherit (lib.systems.examples) mingwW64;
   } // lib.optionalAttrs (system == "x86_64-linux") {