Correct YAML syntax

.github/workflows/build.yaml

@@ -173,7 +173,7 @@ jobs:
           - 2
           - 4
           - 8
-      exclude:
+        exclude:
           # GitHub's macOS 14+ gcc can only target arm64, but Qt didn't add Apple arm64 support until Qt 6.2, so:
           # Exclude Qt 5.x (and 6.0, 6.1) with GCC on macOS 14+. Also see the `arch` step below for more details.
           - { qt: '5.9.9',   os: macos-14, cc: gcc }