ci: build i686-unknown-linux-gnu distributions

These were all being filtered out after PGO was removed.

Author: indygreg

.github/workflows/linux.yml

@@ -136,8 +136,7 @@ jobs:
           - 'pgo'
           - 'pgo+lto'
         exclude:
-          # We don't publish noopt builds for GNU Linux.
-          - triple: 'i686-unknown-linux-gnu'
+          # We don't publish noopt builds for GNU Linux when PGO is available.
           - triple: 'x86_64-unknown-linux-gnu'
             optimizations: 'noopt'
           # PGO doesn't work with musl libc.