Disable Go Workspaces when executing 'go list' in agent packaging process

dev-tools/mage/gotool/go.go

@@ -45,12 +45,18 @@
 
 // GetModuleName returns the name of the module.
 func GetModuleName() (string, error) {
-	lines, err := getLines(callGo(nil, "list", "-m"))
+	lines, err := getLines(callGo(
+		// Disabling the Go workspaces prevents 'go list' from listing all
+		// modules within the workspace.
+		map[string]string{"GOWORK": "off"},
+		"list",
+		"-m"))
 	if err != nil {
 		return "", err
 	}
 	if len(lines) != 1 {
-		return "", fmt.Errorf("unexpected number of lines")
+		return "", fmt.Errorf("expected 'go list -m' to return 1 line, got %d",
+			len(lines))
 	}
 	return lines[0], nil
 }
@@ -204,7 +210,7 @@
 	}, cmd, args)
 }
 
 func runGo(cmd string, args *Args) error {
 	return execGoWith(sh.RunWith, cmd, args)
 }