Use small runner for install-compilers workflow

This workflow only downloads and installs pre-built binaries from S3,
so it doesn't need a full 32 vCPU runner. 8 vCPU (small) is sufficient.

🤖 Generated by LLM (Claude, via OpenClaw)

Author: mattgodbolt-molty

.github/workflows/install-compilers.yml

@@ -21,7 +21,7 @@ on:
 
 jobs:
   install:
-    runs-on: ['self-hosted', 'ce', 'linux', 'x64']
+    runs-on: ['self-hosted', 'ce', 'linux', 'x64', 'small']
     steps:
       - name: Start from a clean directory
         uses: AutoModality/action-clean@v1.1.0