nix: fix incramental flags, again

I'm blind *and* stupid. Cheers!

Author: NotAShelf

nix/packages/anyrun.nix

@@ -70,7 +70,7 @@ in
       then pname
       else null;
 
-    CARGO_BUILD_INCREMENTAL = 0;
+    CARGO_BUILD_INCREMENTAL = "false";
     RUST_BACKTRACE = "full";
 
     postInstall = ''

nix/packages/plugin.nix

@@ -60,7 +60,7 @@ in
     cargoBuildFlags = ["-p ${name}"];
     buildAndTestSubdir = "plugins/${name}";
 
-    CARGO_BUILD_INCREMENTAL = 0;
+    CARGO_BUILD_INCREMENTAL = "false";
     RUST_BACKTRACE = "full";
 
     meta = {