Only cancel other builds on main

Ran into an issue where one OS build was missing a dep and caused all the other ones to be canceled. I want to be able to see which succeed/fail individually in development, but consolidate them all in main.

Author: zephraph

.github/workflows/build.yml

@@ -8,6 +8,7 @@ jobs:
     name: Build on ${{ matrix.os }} for ${{ matrix.target }}
     runs-on: ${{ matrix.os }}
     strategy:
+      fail-fast: ${{ github.ref == 'refs/heads/main' }}
       matrix:
         include:
           - os: ubuntu-latest