Bump DeterminateSystems/nix-installer-action from 19 to 20

Bumps [DeterminateSystems/nix-installer-action](https://github.com/determinatesystems/nix-installer-action) from 19 to 20.
- [Release notes](https://github.com/determinatesystems/nix-installer-action/releases)
- [Commits](DeterminateSystems/nix-installer-action@v19...v20)

---
updated-dependencies:
- dependency-name: DeterminateSystems/nix-installer-action
  dependency-version: '20'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/update-code-cursor.yml

@@ -15,7 +15,7 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Set up Nix
-        uses: DeterminateSystems/nix-installer-action@v19
+        uses: DeterminateSystems/nix-installer-action@v20
 
       - name: Run updater
         run: |

.github/workflows/update-cursor-agent.yml

@@ -15,7 +15,7 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Set up Nix
-        uses: DeterminateSystems/nix-installer-action@v19
+        uses: DeterminateSystems/nix-installer-action@v20
 
       - name: Run updater
         run: |