test(llmobs): use DD_LLMOBS_ENABLED in tagger sampling fixtures (#9107)

The sampling tests in #9030 build their own taggers with `{ llmobs:
{ enabled: true } }`, and #8943 renamed that config key to
`DD_LLMOBS_ENABLED` everywhere it could see. The two landed in parallel,
so #8943 normalized the rest of the file but never saw these four
fixtures. On master the tagger now reads `DD_LLMOBS_ENABLED`, finds it
undefined, and returns before registering the span; `Tagger.tagMap.get`
then yields undefined and the "DROPPED at sampleRate 0" test throws
synchronously, aborting the whole `test:llmobs:sdk:ci` run with exit 7.

Fixes: https://github.com/DataDog/dd-trace-js/actions/runs/28265509637/job/83751636644

Author: BridgeAR

packages/dd-trace/test/llmobs/tagger.spec.js

@@ -196,7 +196,7 @@ describe('tagger', () => {
         })
 
         it('records a DROPPED decision on a root span when sampleRate is 0', () => {
-          tagger = new Tagger({ llmobs: { enabled: true, mlApp: 'my-default-ml-app', sampleRate: 0 } })
+          tagger = new Tagger({ llmobs: { DD_LLMOBS_ENABLED: true, mlApp: 'my-default-ml-app', sampleRate: 0 } })
           tagger.registerLLMObsSpan(span, { kind: 'llm' })
 
           const tags = Tagger.tagMap.get(span)
@@ -206,15 +206,15 @@ describe('tagger', () => {
 
         it('truncates a longer rate to at most 6 decimals', () => {
           // 1/3 = 0.3333... which must be capped at 6 decimal places.
-          tagger = new Tagger({ llmobs: { enabled: true, mlApp: 'my-default-ml-app', sampleRate: 1 / 3 } })
+          tagger = new Tagger({ llmobs: { DD_LLMOBS_ENABLED: true, mlApp: 'my-default-ml-app', sampleRate: 1 / 3 } })
           tagger.registerLLMObsSpan(span, { kind: 'llm' })
 
           assert.strictEqual(Tagger.tagMap.get(span)['_ml_obs.sample_rate'], '0.333333')
         })
 
         it('strips trailing zeros from a fractional rate', () => {
           // 0.25 -> "0.250000" via toFixed(6), which must be stripped back to "0.25".
-          tagger = new Tagger({ llmobs: { enabled: true, mlApp: 'my-default-ml-app', sampleRate: 0.25 } })
+          tagger = new Tagger({ llmobs: { DD_LLMOBS_ENABLED: true, mlApp: 'my-default-ml-app', sampleRate: 0.25 } })
           tagger.registerLLMObsSpan(span, { kind: 'llm' })
 
           assert.strictEqual(Tagger.tagMap.get(span)['_ml_obs.sample_rate'], '0.25')
@@ -253,7 +253,7 @@ describe('tagger', () => {
           // The tagger reads sampleRate from config on each root decision, so a
           // mutation (such as a future remote config update) takes effect without
           // re-instantiating the tagger.
-          const config = { llmobs: { enabled: true, mlApp: 'my-default-ml-app', sampleRate: 1 } }
+          const config = { llmobs: { DD_LLMOBS_ENABLED: true, mlApp: 'my-default-ml-app', sampleRate: 1 } }
           tagger = new Tagger(config)
 
           tagger.registerLLMObsSpan(span, { kind: 'llm' })