Fix error: Stable 1.88.0 is not available in Nix flake

[levydsa]

Fixed by just updating with nix flake update.

error:
       … while calling the 'derivationStrict' builtin
         at <nix/derivation-internal.nix>:37:12:
           36|
           37|   strict = derivationStrict drvAttrs;
             |            ^
           38|

       … while evaluating derivation 'nix-shell'
         whose name attribute is located at /nix/store/wshnc0kqk1qz7iffb1yqri8a5cy6v7w5-source/pkgs/stdenv/generic/make-derivation.nix:375:7

       … while evaluating attribute '__impureHostDeps' of derivation 'nix-shell'
         at /nix/store/wshnc0kqk1qz7iffb1yqri8a5cy6v7w5-source/pkgs/stdenv/generic/make-derivation.nix:490:7:
          489|       __propagatedSandboxProfile = unique (computedPropagatedSandboxProfile ++ [ propagatedSandboxProfile ]);
          490|       __impureHostDeps = computedImpureHostDeps ++ computedPropagatedImpureHostDeps ++ __propagatedImpureHostDeps ++ __impureHostDeps ++ stdenv.__extraImpureHostDeps ++ [
             |       ^
          491|         "/dev/zero"

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: Stable 1.88.0 is not available