[Bug]: toString() on XML fails after adding attribute with default namespace

[rdulmina]

Description

import ballerina/io;

xmlns "http://sample.com/wso2/c1";

public function main() {
    xml x1 = xml `<root xmlns:ns3="http://sample.com/wso2/f"></root>`;
    var xAttr = let var x2 = <'xml:Element>x1 in x2.getAttributes();
    //adding attribute with default namespace
    xAttr["{http://sample.com/wso2/c1}foo1"] = "bar1";
    io:println(x1);
}

Gives

error: io.ballerina.runtime.internal.util.exceptions.BallerinaException {"message":"failed to get xml as string: {ballerina/lang.xml}XMLOperationError"}
        at ballerina.lang.value.0:toString(value.bal:188)
           ballerina.io.1.PrintableClassImpl:toString(print.bal:111)
           ballerina.io.1:externPrintln(print.bal:147)
           ballerina.io.1:println(print.bal:65)
           test:main(test.bal:10)

Need to enable XMLAttributesTest.testAddAttributeWithQName_5, XMLAttributesTest.testAddNamespaceAsAttribute1 after fixing this.

Affected Version(s)

No response

OS, DB, other environment details and versions

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Related area

-> Runtime

Related issue(s) (optional)

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Suggested label(s) (optional)

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Suggested assignee(s) (optional)

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      - Reason/EngineeringMistake - The issue occurred due to a mistake made in the past.
      - Reason/Regression - The issue has introduced a regression.
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      - Reason/Complex - Issue occurred due to complex scenario.
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      - Reason/Other - None of the above cases.