Disable Go Workspaces when executing 'go list' in agent packaging process (#4039) (#4113)

running 'go list' with Go worspaces enabled will report all modules listed on go.work, what would make GetModuleName to fail as it requires 'go list' to return only one module, the agent itself.

(cherry picked from commit bccb12e)

Co-authored-by: Anderson Queiroz <anderson.queiroz@elastic.co>

Author: mergify[bot]

dev-tools/mage/gotool/go.go

@@ -45,12 +45,18 @@ var Test goTest = runGoTest
 
 // 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
 }