ci: test non-cgo packages in 32-bit mode

This commit runs Gio's test harness in 32-bit mode as well as 64-bit. This helps
catch bugs in Gio and its dependencies where integer overflow causes build or
runtime problems.

The complexities of cross-compiling CGO made it prohibitively difficult to test
all of Gio, so these changes only run tests for packages in pure Go.

References: https://todo.sr.ht/~eliasnaur/gio/384
Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

.builds/linux.yml

@@ -57,6 +57,7 @@ tasks:
  - test_gio: |
      cd gio
      go test -race ./...
+     CGO_ENABLED=1 GOARCH=386 go test ./{f32,font,gesture,io,layout,op,text,unit,widget}/...
      GOOS=windows go test -exec=wine ./...
      GOOS=js GOARCH=wasm go build -o /dev/null ./...
  - install_chrome: |