Bump cachix/install-nix-action from 20 to 27

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 20 to 27.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@v20...V27)

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

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

.github/workflows/formatting.yml

@@ -14,7 +14,7 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v20
+      - uses: cachix/install-nix-action@V27
 
       - name: Format
         run: nix develop --command treefmt --fail-on-change

.github/workflows/koishi.yml

@@ -23,7 +23,7 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v20
+      - uses: cachix/install-nix-action@V27
 
       - name: Clippy
         run: nix develop --command cargo clippy -- -Dwarnings
@@ -37,7 +37,7 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v20
+      - uses: cachix/install-nix-action@V27
 
       - name: Clippy
         run: nix develop --command cargo clippy -- -Dwarnings
@@ -51,7 +51,7 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v20
+      - uses: cachix/install-nix-action@V27
 
       - name: Clippy
         run: nix develop --command cargo clippy -- -Dwarnings
@@ -62,7 +62,7 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v20
+      - uses: cachix/install-nix-action@V27
 
       - name: Build
         working-directory: ./koishi/firmware
@@ -83,7 +83,7 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v20
+      - uses: cachix/install-nix-action@V27
 
       - name: Build
         working-directory: ./koishi/firmware