[PhingTask] Fixed multi same property

[siad007]

Fixed following behavior:

    <target name="multi-same-property">
        <phing phingfile="phing.xml" target="echo-for-multi-same">
            <property name="prop" value="one"/>
            <property name="prop" value="two"/>
        </phing>
    </target>

    <target name="echo-for-multi-same">
        <echo>prop is ${prop}</echo>
    </target>

will output:

prop is one
prop is one

Related to #1241

[codecov]

Codecov Report

Merging #1296 into master will increase coverage by 0.00%.
The diff coverage is 85.18%.

@@            Coverage Diff            @@
##             master    #1296   +/-   ##
=========================================
  Coverage     51.21%   51.21%           
- Complexity     9302     9306    +4     
=========================================
  Files           479      479           
  Lines         22751    22753    +2     
=========================================
+ Hits          11652    11654    +2     
  Misses        11099    11099           

Impacted Files	Coverage Δ	Complexity Δ
classes/phing/tasks/system/ForeachTask.php	68.98% <ø> (-0.77%)	56.00 <0.00> (ø)
classes/phing/tasks/system/PhingTask.php	74.89% <85.18%> (+0.65%)	91.00 <0.00> (+4.00)

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