chore: run nix flake update (#1437)

From time to time, we should make sure to also update the flake we're
using to create our own.

#### What this PR does / why we need it

When switching to the latest patch version of go, sometimes the action
fails:
https://github.com/open-component-model/ocm/actions/runs/14731906561

So we need to ensure, the file:
https://github.com/open-component-model/ocm/blob/main/flake.lock get's
updated as well. Which is done by: `nix flake update`

Author: hilmarf

.github/workflows/flake_vendorhash.yaml

@@ -29,6 +29,8 @@ jobs:
         uses: DeterminateSystems/nix-installer-action@v17
         with:
           nix-package-url: https://releases.nixos.org/nix/nix-2.26.2/nix-2.26.2-x86_64-linux.tar.xz
+      - name: Update flake.lock
+        run: nix flake update
       - name: Update ocm vendor hash
         run: nix run .#nixpkgs.nix-update -- --flake --version=skip ocm
       - name: Check diff and create action summary