fix: use sh instead of bash and replace checkout action with git

- Use sh (built into Alpine) instead of bash to avoid install errors
- Replace actions/checkout@v4 with direct git clone commands
- Add ca-certificates for HTTPS support
- Faster and more reliable for lightweight Alpine containers

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.gitea/workflows/build.yaml

@@ -13,19 +13,25 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Install dependencies
+        shell: sh
         run: |
-          apk add --no-cache bash wget
+          apk add --no-cache git wget ca-certificates
 
       - name: Install Kaniko
+        shell: sh
         run: |
           wget -O /usr/local/bin/executor https://github.com/GoogleContainerTools/kaniko/releases/download/v1.23.2/executor-linux-amd64
           chmod +x /usr/local/bin/executor
 
       - name: Checkout code
-        uses: actions/checkout@v4
+        shell: sh
+        run: |
+          git clone https://gitea.leeworks.dev/${{ gitea.repository }}.git .
+          git checkout ${{ gitea.sha }}
 
       - name: Determine image tags
         id: tags
+        shell: sh
         run: |
           REGISTRY="gitea.leeworks.dev"
           REPO_OWNER="${{ gitea.repository_owner }}"
@@ -62,6 +68,7 @@ jobs:
           echo "IMAGE_LATEST=${IMAGE_BASE}:latest" >> $GITHUB_OUTPUT
 
       - name: Setup Kaniko config
+        shell: sh
         run: |
           mkdir -p /kaniko/.docker
           cat > /kaniko/.docker/config.json <<EOF
@@ -75,6 +82,7 @@ jobs:
           EOF
 
       - name: Build and push with Kaniko
+        shell: sh
         run: |
           echo "Building and pushing image with Kaniko..."
           if [[ "${{ steps.tags.outputs.PUSH_LATEST }}" == "true" ]]; then