chore(deps): bump cachix/install-nix-action from 30 to 31

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 30 to 31.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](cachix/install-nix-action@v30...v31)

---
updated-dependencies:
- dependency-name: cachix/install-nix-action
  dependency-version: '31'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/build-main.yml

@@ -41,7 +41,7 @@ jobs:
               uses: actions/checkout@v4
 
             - name: Install Nix
-              uses: cachix/install-nix-action@v30
+              uses: cachix/install-nix-action@v31
 
             - name: Build document
               run: |

.github/workflows/build-pr.yml

@@ -20,7 +20,7 @@ jobs:
               uses: actions/checkout@v4
 
             - name: Install Nix
-              uses: cachix/install-nix-action@v30
+              uses: cachix/install-nix-action@v31
 
             - name: Extract branch name
               shell: bash