disable 128-bit trace id generation in CI mode

[anmarchenko]

What does this PR do?
Disables 128-bit trace_id generation for CI mode. Tracing enabled it by default in DataDog/dd-trace-rb#3266

Motivation
128-bit trace ids cause message pack to fail with "Cause: bignum too big to convert into `unsigned long long'" causing agentless mode to fail completely

How to test the change?

git clone https://github.com/DataDog/test-environment

cd test-environment

yarn

cd dd-trace-rb/jekyll
bundle add ddtrace --git "https://github.com/DataDog/dd-trace-rb.git" --branch "master" --skip-install
bundle install --path .bundle
cd ../..

yarn test dd-trace-rb/jekyll.test.js

cd dd-trace-rb/devdocs
bundle add ddtrace --git "https://github.com/DataDog/dd-trace-rb.git" --branch "master" --skip-install
bundle install --path .bundle
cd ../..

yarn test dd-trace-rb/devdocs.test.js