fix(axiom): ensure unnamed spans are not recorded

[hahuja2]

This PR adds a fix that ensures only named segments are pushed to the span_queue. This ensures that unnamed spans are not recorded.

[newrelic-php-agent-bot]

Test Suite	Status	Result
Multiverse	✅	18/18 passing
SOAK	✅	135/135 passing

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.06%. Comparing base (18174dd) to head (b37e028).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1197   +/-   ##
=======================================
  Coverage   80.05%   80.06%           
=======================================
  Files         189      189           
  Lines       27699    27699           
=======================================
+ Hits        22174    22176    +2     
+ Misses       5525     5523    -2     

Flag	Coverage Δ
agent-for-php-7.2	79.97% <100.00%> (ø)
agent-for-php-7.3	79.99% <100.00%> (?)
agent-for-php-7.4	79.86% <100.00%> (ø)
agent-for-php-8.0	79.45% <100.00%> (ø)
agent-for-php-8.1	79.67% <100.00%> (ø)
agent-for-php-8.2	79.27% <100.00%> (ø)
agent-for-php-8.3	79.35% <100.00%> (ø)
agent-for-php-8.4	79.37% <100.00%> (ø)
agent-for-php-8.5	78.68% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.