Fixed PHPDoc code example in session/adapter/files

[Jeckerson]

Hello!

• Type: documentation
• Link to issue:

In raising this pull request, I confirm the following:

• I have read and understood the Contributing Guidelines
• I have checked that another pull request for this purpose does not exist
• I wrote some tests for this PR
• I updated the CHANGELOG

Thanks

[codecov]

Codecov Report

Merging #14031 into 4.0.x will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            4.0.x   #14031   +/-   ##
=======================================
  Coverage   68.51%   68.51%           
=======================================
  Files         470      470           
  Lines       95155    95155           
=======================================
  Hits        65197    65197           
  Misses      29958    29958

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[sergeyklay]

Thank you