ci: run go unit tests from the dagger plan

Signed-off-by: Sam Alba <samalba@users.noreply.github.com>

pkg/universe.dagger.io/go/image.cue

@@ -13,7 +13,11 @@ _#DefaultVersion: "1.18"
 
 	packages: [pkgName=string]: version: string | *""
 	// FIXME Remove once golang image include 1.18 *or* go compiler is smart with -buildvcs
-	packages: git: _
+	packages: {
+		git: _
+		// For GCC and other possible build dependencies
+		"alpine-sdk": _
+	}
 
 	// FIXME Basically a copy of alpine.#Build with a different image
 	// Should we create a special definition?