pius: perl should be a runtime dependency, not a build-time one

Since 61bc03c017, patch-shebangs
now distinguishes between build-time and runtime dependencies.

Prior to this commit, perl was not being placed in patch-shebangs'
search path when it is run during the fixup phase.

pkgs/tools/security/pius/default.nix

@@ -19,7 +19,7 @@ python3Packages.buildPythonApplication {
     done
   '';
 
-  nativeBuildInputs = [ perl ];
+  buildInputs = [ perl ];
 
   meta = {
     homepage = https://www.phildev.net/pius/;