[PHPUnitTask] Fixed processIsolation setting

[siad007]

Added missing process isolation setting for test suite.

[codecov]

Codecov Report

Merging #1451 (d2bc053) into master (7a3d331) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master    #1451   +/-   ##
=========================================
  Coverage     53.85%   53.85%           
  Complexity     9202     9202           
=========================================
  Files           469      469           
  Lines         22337    22338    +1     
=========================================
+ Hits          12030    12031    +1     
  Misses        10307    10307           

Impacted Files	Coverage Δ	Complexity Δ
...ses/phing/tasks/ext/phpunit/PHPUnitTestRunner9.php	48.69% <100.00%> (+0.45%)	53.00 <0.00> (ø)

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