Fix workflow: install gobjc before compile.

Author: badmonster0

.github/workflows/CI.yml

@@ -43,4 +43,7 @@ jobs:
           args: --release --out dist --find-interpreter
           sccache: 'true'
           manylinux: auto
+          before-script-linux: |
+            sudo apt-get update
+            sudo apt-get install -y gnustep gnustep-devel gobjc
           container: ${{ matrix.platform.container }}