chore: fix a warning about overrideAttrs usage

trace: evaluation warning: packer-1.13.1 was overridden with `version` but not `src` at /nix/store/y2ddpvhfvv5pshcrj0jckgz36fm9n3c6-source/nix/devShells.nix:49:17.

This is most likely not what you want. In order to properly change the version of a package, override
both the `version` and `src` attributes:

hello.overrideAttrs (oldAttrs: rec {
  version = "1.0.0";
  src = pkgs.fetchurl {
    url = "mirror://gnu/hello/hello-${version}.tar.gz";
    hash = "...";
  };
})

(To silence this warning, set `__intentionallyOverridingVersion = true` in your `overrideAttrs` call.)

Author: yvan-sraka

nix/devShells.nix

@@ -47,6 +47,7 @@
               ansible-lint
               (packer.overrideAttrs (_oldAttrs: {
                 version = "1.7.8";
+                __intentionallyOverridingVersion = true;
               }))
 
               self'.packages.start-server