Bump DeterminateSystems/nix-installer-action from 20 to 21

Bumps [DeterminateSystems/nix-installer-action](https://github.com/determinatesystems/nix-installer-action) from 20 to 21.
- [Release notes](https://github.com/determinatesystems/nix-installer-action/releases)
- [Commits](DeterminateSystems/nix-installer-action@v20...v21)

---
updated-dependencies:
- dependency-name: DeterminateSystems/nix-installer-action
  dependency-version: '21'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/bump.yaml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v6
-    - uses: DeterminateSystems/nix-installer-action@v20
+    - uses: DeterminateSystems/nix-installer-action@v21
       with:
         extra-conf: |
           access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}

.github/workflows/check.yaml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
-      - uses: DeterminateSystems/nix-installer-action@v20
+      - uses: DeterminateSystems/nix-installer-action@v21
         with:
           extra-conf: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}

.github/workflows/lower-init.yaml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v6
-    - uses: DeterminateSystems/nix-installer-action@v20
+    - uses: DeterminateSystems/nix-installer-action@v21
       with:
         extra-conf: |
           access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}

.github/workflows/lower-optimize.yaml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v6
-    - uses: DeterminateSystems/nix-installer-action@v20
+    - uses: DeterminateSystems/nix-installer-action@v21
       with:
         extra-conf: |
           access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}

.github/workflows/lower.yaml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v6
-    - uses: DeterminateSystems/nix-installer-action@v20
+    - uses: DeterminateSystems/nix-installer-action@v21
       with:
         extra-conf: |
           access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}