Bump the determinatesystems-actions group with 2 updates (#214)

Bumps the determinatesystems-actions group with 2 updates: [DeterminateSystems/nix-installer-action](https://github.com/determinatesystems/nix-installer-action) and [DeterminateSystems/magic-nix-cache-action](https://github.com/determinatesystems/magic-nix-cache-action).


Updates `DeterminateSystems/nix-installer-action` from 11 to 12
- [Release notes](https://github.com/determinatesystems/nix-installer-action/releases)
- [Commits](DeterminateSystems/nix-installer-action@v11...v12)

Updates `DeterminateSystems/magic-nix-cache-action` from 4 to 7
- [Release notes](https://github.com/determinatesystems/magic-nix-cache-action/releases)
- [Commits](DeterminateSystems/magic-nix-cache-action@v4...v7)

---
updated-dependencies:
- dependency-name: DeterminateSystems/nix-installer-action
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: determinatesystems-actions
- dependency-name: DeterminateSystems/magic-nix-cache-action
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: determinatesystems-actions
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/ci-nix.yml

@@ -29,8 +29,8 @@ jobs:
     timeout-minutes: 30
     steps:
       - uses: actions/checkout@v4
-      - uses: DeterminateSystems/nix-installer-action@v11
-      - uses: DeterminateSystems/magic-nix-cache-action@v4
+      - uses: DeterminateSystems/nix-installer-action@v12
+      - uses: DeterminateSystems/magic-nix-cache-action@v7
       - run: nix flake check
       - run: nix develop --command echo 'This step should be done before any other "nix develop" steps because of measuring Nix build time'
       - run: nix develop --command task deps

.github/workflows/reusable-bump-flake-lock-and-selfup.yml

@@ -63,8 +63,8 @@ jobs:
           # Needed to specify token for checkout phase, only in pushing phase is too late
           # https://github.com/orgs/community/discussions/27072#discussioncomment-3254515
           token: ${{ steps.publish-token.outputs.token }}
-      - uses: DeterminateSystems/nix-installer-action@8cdf194da984e4f12b2f8c36d1fa107c1dd67f5c # v11
-      - uses: DeterminateSystems/magic-nix-cache-action@fc6aaceb40b9845a02b91e059ec147e78d1b4e41 # v4
+      - uses: DeterminateSystems/nix-installer-action@7993355175c2765e5733dae74f3e0786fe0e5c4f # v12
+      - uses: DeterminateSystems/magic-nix-cache-action@b46e247b898aa56e6d2d2e728dc6df6c84fdb738 # v7
       - name: Fetch active PRs by me
         id: fetch-active-prs
         env: