Fix integration tests using Predis

[iamluc]

Description

Both scenarios DeferredLoading and Predis were running composer install in the same directory.
It seems it could break the installation

i.e. https://app.circleci.com/pipelines/github/DataDog/dd-trace-php/17446/workflows/0a933327-d943-4704-b7c9-4f9f560cb329/jobs/5142824

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.06%. Comparing base (ebaa1ca) to head (8f066a7).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #2846   +/-   ##
=========================================
  Coverage     81.06%   81.06%           
  Complexity     2516     2516           
=========================================
  Files           146      146           
  Lines         14653    14653           
=========================================
  Hits          11879    11879           
  Misses         2774     2774           

Flag	Coverage Δ
tracer-extension	78.18% <ø> (ø)
tracer-php	82.27% <ø> (ø)

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[bwoebi]

Looks like my mistake, thanks for catching :-)