phpExtensions.{pdo_,}pgsql: fix build

I don't know why, but after the switch to libpq, the builds failed with
an error like

    configure: error: Unable to build the PDO PostgreSQL driver: at least libpq 9.1 is required

and adding `libpq` to build inputs solves the issue.

pkgs/top-level/php-packages.nix

@@ -634,6 +634,7 @@ lib.makeScope pkgs.newScope (
               {
                 name = "pdo_pgsql";
                 internalDeps = [ php.extensions.pdo ];
+                buildInputs = [ libpq ];
                 configureFlags = [ "--with-pdo-pgsql=${lib.getDev libpq}" ];
                 doCheck = false;
               }
@@ -646,7 +647,10 @@ lib.makeScope pkgs.newScope (
               }
               {
                 name = "pgsql";
-                buildInputs = [ pcre2 ];
+                buildInputs = [
+                  pcre2
+                  libpq
+                ];
                 configureFlags = [ "--with-pgsql=${lib.getDev libpq}" ];
                 doCheck = false;
               }