[loader] Fix detection of JIT enabled

[iamluc]

Description

Testing PHP 8.4 with Ondrej PPA, tracer was disabled because opcache.jit is an empty string

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 74.82%. Comparing base (ab52de5) to head (fc04956).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #2971   +/-   ##
=========================================
  Coverage     74.82%   74.82%           
  Complexity     2741     2741           
=========================================
  Files           110      110           
  Lines         10863    10863           
=========================================
  Hits           8128     8128           
  Misses         2735     2735           

Flag	Coverage Δ
tracer-php	74.82% <ø> (ø)

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