ci: install system dependencies in GitHub Actions workflow

Install inotify-tools and poppler-utils in CI environment:
- inotify-tools: Required for file_system library (LibraryWatcher)
- poppler-utils: Provides pdfinfo command for PDF metadata extraction

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: jfro

.github/workflows/elixir.yml

@@ -44,6 +44,8 @@ jobs:
         with:
           elixir-version: "1.18" # [Required] Define the Elixir version
           otp-version: "27.0" # [Required] Define the Erlang/OTP version
+      - name: Install system dependencies
+        run: sudo apt-get update && sudo apt-get install -y inotify-tools poppler-utils
       - name: Restore dependencies cache
         uses: actions/cache@0400d5f644dc74513175e3cd8d07132dd4860809 # v4.2.4
         with: