fix(ci): install gcc and zlib headers for native-image compilation

GraalVM native-image requires a C compiler (gcc) and zlib dev
headers to compile native binaries. The maven:3.9.6-eclipse-temurin-21
image is JDK-only and lacks these build tools, causing the build
to fail with:

  Error: Default native-compiler executable 'gcc' not found via PATH

Extend the install step with build-essential (gcc, g++, make)
and zlib1g-dev so the native-image pipeline has the required
toolchain.

.gitea/workflows/ci.yml

@@ -20,15 +20,16 @@ jobs:
     container:
       image: maven:3.9.6-eclipse-temurin-21
     steps:
-      - name: Install git, node, and basic tools
+      - name: Install git, node, gcc, and basic tools
         run: |
           apt-get update
-          apt-get install -y git curl ca-certificates
+          apt-get install -y git curl ca-certificates build-essential zlib1g-dev
           curl -fsSL https://deb.nodesource.com/setup_22.x | bash -
           apt-get install -y nodejs
           rm -rf /var/lib/apt/lists/*
           git --version
           node --version
+          gcc --version
 
       - name: Checkout
         uses: actions/checkout@v4