ci: ci-fresh-install — fix GCC version, remove PR trigger

- GCC: don't set toolchain default (GCC is already default after
  xlings install mcpp), fixes "gcc@ is not installed" error
- Remove pull_request trigger: ci-fresh-install tests released mcpp
  (not PR code), so it should not block PRs. Runs on push to main,
  workflow_dispatch, and daily schedule only.

Author: Sunrisepeak

.github/workflows/ci-fresh-install.yml

@@ -7,14 +7,13 @@ name: ci-fresh-install
 #   1. mcpp new hello → mcpp run (basic project)
 #   2. mcpp build (build mcpp itself from source)
 #
-# This workflow does NOT run on PRs — it tests released mcpp, not PR code.
-# Triggered manually or on a schedule to catch regressions after releases.
+# This workflow tests released mcpp, not PR code.
+# It does NOT run on PRs — only on push to main, manual trigger, and daily schedule.
+# Failures here mean the released mcpp has issues, not that the PR is broken.
 
 on:
   push:
     branches: [ main ]
-  pull_request:
-    branches: [ main ]
   workflow_dispatch:
   schedule:
     # Run daily at 06:00 UTC to catch issues from xlings/runner updates
@@ -48,15 +47,13 @@ jobs:
 
       - name: "GCC: mcpp new → run"
         run: |
-          mcpp toolchain default gcc
           cd "$(mktemp -d)"
           mcpp new hello_gcc
           cd hello_gcc
           mcpp run
 
       - name: "GCC: build mcpp"
         run: |
-          mcpp toolchain default gcc
           mcpp clean
           mcpp build