autoprefixer.tests: fix the eval

Without the change thee val fails as:

    $ nix build --no-link -f. autoprefixer.tests
    ...
       error: attribute 'packageName' missing
       at pkgs/by-name/au/autoprefixer/tests/simple-execution.nix:4:26:
            3| let
            4|   inherit (autoprefixer) packageName version;
             |                          ^
            5| in

pkgs/by-name/au/autoprefixer/tests/simple-execution.nix

@@ -1,10 +1,10 @@
 { runCommand, autoprefixer }:
 
 let
-  inherit (autoprefixer) packageName version;
+  inherit (autoprefixer) pname version;
 in
 
-runCommand "${packageName}-tests" { meta.timeout = 60; }
+runCommand "${pname}-tests" { meta.timeout = 60; }
   ''
     # get version of installed program and compare with package version
     claimed_version="$(${autoprefixer}/bin/autoprefixer --version | awk '{print $2}')"