[TEST] fix test failure with elasticsearch exporter on cxx20

[dbarker]

Fixes #3278

Changes

Removes the conditional that switches to std::format on cxx20 in es_log_recordable.cc.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[netlify]

✅ Deploy Preview for opentelemetry-cpp-api-docs canceled.

Name	Link
🔨 Latest commit	bc67a28
🔍 Latest deploy log	https://app.netlify.com/sites/opentelemetry-cpp-api-docs/deploys/67e110fa2f268200080607ab

[dbarker]

Steps to reproduce the elasticsearch exporter test failure in a linux container.

1. build and run a dev container setting CXX_STANDARD=20.

cd <path-to-opentelemetry-cpp>
docker build --build-arg CXX_STANDARD=20 --build-arg USER_UID="$(id -u)" --build-arg USER_GID="$(id -g)"  -t opentelemetry-cpp-dev:cxx20 -f ./.devcontainer/Dockerfile.dev .
docker run -it -v "$PWD:/workspaces/opentelemetry-cpp" opentelemetry-cpp-dev:cxx20 bash

2. build the elasticsearch exporter and run tests

cmake -S . -B ~/build -DWITH_ELASTICSEARCH=ON
cmake --build ~/build 
ctest --test-dir ~/build

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.52%. Comparing base (2c9b68f) to head (bc67a28).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3308      +/-   ##
==========================================
+ Coverage   89.50%   89.52%   +0.02%     
==========================================
  Files         210      210              
  Lines        6522     6522              
==========================================
+ Hits         5837     5838       +1     
+ Misses        685      684       -1     

see 1 file with indirect coverage changes

🚀 New features to boost your workflow:

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

[marcalff]

LGTM, thanks for the fix.