Fix a bug in the definition of the PML postprocessing results that was...

Description

Fix a bug in the definition of the PML postprocessing results that was introduced along with the curvilinear PML implementation. The postprocessing coeffunctions were set to be always complex, leading to an error when a transient PML was applied Testsuite merge request: ( no Testsuite changes | paste a link to the Testsuite merge request )

Check before assigning to a maintainer for review

• The history is clean
• New Code is well-documented and understandable
• There is a test case (in case of new functionality)
• Every commit passes the pipeline

Maintainer checks before merge

• Review is approved, and all comments are resolved
• Check for Testsuite changes, if yes check
  • Testsuite merge request merges fast-forward
  • Testsuite-submodule SHA of every CFS commit references a commit in Testsuite Merge Request
  • Testsuite-submodule SHA of last CFS commit points to HEAD of corresponding Testsuite branch
• Pipeline passes for every commit
  • all tests of the stage test pass
  • tests in the stage test_extra run
  • new tests are actually running (e.g. check if they appear on CDash)