build(deps): bump cachix/install-nix-action from 20 to 28

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 20 to 28.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@v20...V28)

---
updated-dependencies:
- dependency-name: cachix/install-nix-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/lint.yml

@@ -57,7 +57,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: cachix/install-nix-action@v20
+      - uses: cachix/install-nix-action@V28
       - uses: cachix/cachix-action@v12
         with:
           name: ethermint
@@ -73,7 +73,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: cachix/install-nix-action@v20
+      - uses: cachix/install-nix-action@V28
       - uses: cachix/cachix-action@v12
         with:
           name: ethermint

.github/workflows/test.yml

@@ -87,7 +87,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: cachix/install-nix-action@v20
+      - uses: cachix/install-nix-action@V28
       - uses: cachix/cachix-action@v12
         with:
           name: ethermint
@@ -122,7 +122,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3
-      - uses: cachix/install-nix-action@v20
+      - uses: cachix/install-nix-action@V28
       - uses: cachix/cachix-action@v12
         with:
           name: ethermint