chore(deps): update determinatesystems/nix-installer-action action to v21

Author: renovate[bot]

.github/actions/set_up_runner/action.yaml

@@ -7,7 +7,7 @@ inputs:
 runs:
   using: composite
   steps:
-    - uses: DeterminateSystems/nix-installer-action@786fff0690178f1234e4e1fe9b536e94f5433196 # v20
+    - uses: DeterminateSystems/nix-installer-action@c5a866b6ab867e88becbed4467b93592bce69f8a # v21
       with:
         github-token: ${{ inputs.github_token }}
     - uses: DeterminateSystems/magic-nix-cache-action@565684385bcd71bad329742eefe8d12f2e765b39 # v13