ci: simplify workflow - use current directory (repo auto-checked-out)

Previous failure: git clone tried to clone into /workspace which already exists

Fix:
- Remove git clone step
- Forgejo automatically checks out repo into current directory
- Just install git, get commit info, build, and push
- Much simpler and cleaner

.gitea/workflows/build.yaml

@@ -13,19 +13,15 @@ jobs:
       image: docker:27-dind
       options: --privileged
     steps:
-      - name: Checkout code
+      - name: Install git
         run: |
           apk add --no-cache git
-          git clone https://git.riotpiao.com:2222/rock/poimen-memory.git /workspace
-          cd /workspace
-          git checkout ${{ github.sha }}
 
       - name: Get commit info
         id: info
         run: |
-          cd /workspace
+          SHORT_SHA=$(git -C . rev-parse --short HEAD)
-          SHORT_SHA=$(git rev-parse --short HEAD)
+          COMMIT_MSG=$(git -C . log -1 --pretty=%B | head -1)
-          COMMIT_MSG=$(git log -1 --pretty=%B | head -1)
           echo "short_sha=${SHORT_SHA}" >> $GITHUB_OUTPUT
           echo "commit_msg=${COMMIT_MSG}" >> $GITHUB_OUTPUT
           echo "Building: ${SHORT_SHA} - ${COMMIT_MSG}"
@@ -37,7 +33,6 @@ jobs:
 
       - name: Build image
         run: |
-          cd /workspace
           docker build \
             --tag forgejo.riotpiao.com/rock/poimen-memory:${{ steps.info.outputs.short_sha }} \
             --tag forgejo.riotpiao.com/rock/poimen-memory:latest \