pypy27Packages.pluthon: fix eval

Without the change the eval fails to concatenate lists as:

    $ nix build --no-link -f. pypy27Packages.pluthon
    error:
       … while evaluating the attribute 'drvPath'
         at lib/customisation.nix:365:7:
          364|     in commonAttrs // {
          365|       drvPath = assert condition; drv.drvPath;
             |       ^
          366|       outPath = assert condition; drv.outPath;

       … while evaluating the attribute 'drvPath'
         at lib/customisation.nix:365:7:
          364|     in commonAttrs // {
          365|       drvPath = assert condition; drv.drvPath;
             |       ^
          366|       outPath = assert condition; drv.outPath;

       … while calling the 'derivationStrict' builtin
         at <nix/derivation-internal.nix>:9:12:
            8|
            9|   strict = derivationStrict drvAttrs;
             |            ^
           10|

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: expected a list but found a set: { type = "derivation"; LANG = «thunk»; __ignoreNulls = true; __structuredAttrs = «thunk»; all = «thunk»; args = «thunk»; buildInputs = «thunk»; builder = «thunk»; cmakeFlags = «thunk»; configureFlags = «thunk»; «45 attributes elided» }

pkgs/development/python-modules/pluthon/default.nix

@@ -26,7 +26,7 @@ buildPythonPackage rec {
     setuptools
     uplc
     ordered-set
-  ] ++ lib.optionals (pythonOlder "3.9") graphlib-backport;
+  ] ++ lib.optional (pythonOlder "3.9") graphlib-backport;
 
   pythonImportsCheck = [ "pluthon" ];