Update the validation logic for the package name:

- When using the project name, allow underscore (`_`) characters
- Send a warning instead of an error when the project name is modified to fit the package name format

(cherry picked from commit 0325568a9b)

platform/android/export/export_plugin.cpp

@@ -456,7 +456,7 @@ String EditorExportPlatformAndroid::get_valid_basename() const {
 		if (is_digit(c) && first) {
 			continue;
 		}
-		if (is_ascii_alphanumeric_char(c)) {
+		if (is_ascii_identifier_char(c)) {
 			name += String::chr(c);
 			first = false;
 		}
@@ -533,13 +533,6 @@ bool EditorExportPlatformAndroid::is_package_name_valid(const String &p_package,
 		return false;
 	}
 
-	if (p_package.find("$genname") >= 0 && !is_project_name_valid()) {
-		if (r_error) {
-			*r_error = TTR("The project name does not meet the requirement for the package name format. Please explicitly specify the package name.");
-		}
-		return false;
-	}
-
 	return true;
 }
 
@@ -2435,6 +2428,13 @@ bool EditorExportPlatformAndroid::has_valid_project_configuration(const Ref<Edit
 		err += "\n";
 	}
 
+	String package_name = p_preset->get("package/unique_name");
+	if (package_name.find("$genname") >= 0 && !is_project_name_valid()) {
+		// Warning only, so don't override `valid`.
+		err += vformat(TTR("The project name does not meet the requirement for the package name format and will be updated to \"%s\". Please explicitly specify the package name if needed."), get_valid_basename());
+		err += "\n";
+	}
+
 	r_error = err;
 	return valid;
 }