tree-wide: fix instance of "meta.maintainer" -> "meta.maintainers"

Encountered one of these when using check-meta, did a quick
search to find other instances.

pkgs/misc/vscode-extensions/python/default.nix

@@ -36,6 +36,6 @@ vscode-utils.buildVscodeMarketplaceExtension {
 
     meta = with lib; {
       license = licenses.mit;
-      maintainer = [ maintainers.jraygauthier ];
+      maintainers = [ maintainers.jraygauthier ];
     };
-}
+}