chore: nix flake update

Updated nixpkgs to 25.05
Replaced flake postgresql dependency with much smaller libpq.
Updated Cargo dependencies due to vulnerability found in tonic, see https://rustsec.org/advisories/RUSTSEC-2025-0009
Utilise new inputs.self.submodules feature to simplify flake use
Changelog-None

Author: JosephGoulden

.github/workflows/ci.yaml

@@ -607,11 +607,11 @@ jobs:
       - name: Check Nix flake inputs
         uses: DeterminateSystems/flake-checker-action@v8
       - name: Install Nix
-        uses: cachix/install-nix-action@V27
+        uses: cachix/install-nix-action@v31
         with:
-          nix_path: nixpkgs=channel:nixos-24.05
+          nix_path: nixpkgs=channel:nixos-25.05
       - name: Check flake
-        run: nix flake check .?submodules=1#
+        run: nix flake check
 
   gather:
     # A dummy task that depends on the full matrix of tests, and