Fix workflow: install gobjc before compile.

Author: badmonster0

.github/workflows/CI.yml

@@ -12,12 +12,14 @@ on:
       - src/**
       - python/**
       - "*.toml"
+      - ".github/workflows/CI.yml"
   push:
     branches: [main]
     paths:
       - src/**
       - python/**
       - "*.toml"
+      - ".github/workflows/CI.yml"
   workflow_dispatch:
 
 permissions:
@@ -43,4 +45,7 @@ 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 }}