Fix property placeholder at maxConcurrency

[SGmuwa]

At version 4.2.0 maven send error when use a property placeholder at maxConcurrency in parallel-foreach:

Failed to execute goal org.mule.tools.maven:mule-maven-plugin:4.2.0:process-classes (default-process-classes) on project myAwasomeProjectName: A type incompatibility occurred while executing org.mule.tools.maven:mule-maven-plugin:4.2.0:process-classes: class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')

To reproduce the error:
First, create xml app:

<?xml version="1.0" encoding="utf-8"?>
<mule xmlns="http://www.mulesoft.org/schema/mule/core"
      xmlns:doc="http://www.mulesoft.org/schema/mule/documentation"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd">
    <global-property doc:id="ce54453a-9fb3-47d7-a666-a47fba7fd11b"
                     doc:name="Global Property"
                     name="maxConcurrency"
                     value="2" />
    <flow doc:id="13ba605b-3247-4b85-8dc2-1a0d0ea228c5"
          name="test-placeholders-numbersFlow">
        <scheduler doc:id="992a3443-7759-4276-8d83-f7e9d75804aa"
                   doc:name="Scheduler">
            <scheduling-strategy>
                <fixed-frequency />
            </scheduling-strategy>
        </scheduler>
        <parallel-foreach collection="#[1 to 2]"
                          doc:id="f82c6c5d-6052-4506-8df0-6805c9b8dfec"
                          doc:name="Parallel For Each"
                          maxConcurrency="${maxConcurrency}">
            <logger doc:id="8cd531ff-89d1-47d5-b750-a074e90dceb6"
                    doc:name="Logger"
                    level="INFO" />
        </parallel-foreach>
    </flow>
</mule>

secondly, change mule-maven-plugin from 4.1.2 → 4.2.0

Thirdly, start mvn package.

references:

1. https://bradmcnaughton.com/mule-maven-plugin-type-incompatibility
2. https://help.mulesoft.com/s/question/0D56R00009IZXY0SAP/error-failed-to-execute-goal-orgmuletoolsmavenmulemavenplugin420processclasses-defaultprocessclasses-on-project-in-mule-4
3. https://issues.salesforce.com/issue/a028c00000zIzIlAAK/