Update dependency gcovr to v8.6

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
gcovr	==8.5 → ==8.6

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Release Notes

gcovr/gcovr (gcovr)

v8.6

Compare Source

Breaking changes:

• Drop support for Python 3.9. (:issue:1227)

New features and notable changes:

• Add support for Python 3.14. (:issue:1227)

Bug fixes and small improvements:

• To avoid merge errors, add the line number to the name of the unknown function. (:issue:1229)
• If intermediate files are kept, rename the gcov files before processing them to log the
  final filename. (:issue:1230)
• Use the first line after a function definition and not the first line which is hit. (:issue:1231)

.. _release_8_5:

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