* ci(codspeed): pin benchmark runner to ubuntu-24.04
ubuntu-latest resolves to different runner images between the BASE
(main/staging) and HEAD (PR) runs, so CodSpeed reports 'Different
runtime environments detected' and emits false-positive regressions
(e.g. a -25.2% swing on test_completion_multi_turn in #31684, an MCP
auth fix with no LLM code changes). Pinning the runner to a fixed
image keeps BASE and HEAD on the same hardware so 1 ms swings on a
~3 ms benchmark stop blocking unrelated PRs.
Fixes#31738
* ci(codspeed): stop running benchmarks on litellm_internal_staging
The CodSpeed check flip-flops on internal staging and on PRs targeting
it (e.g. "+11.75% improvement" on one run, "-25.36% regression" on the
next) because the comparison flags "different runtime environments" and
the benchmarks are only 3-4 ms, so sub-millisecond runner noise swings
the result by 25-30%. Pinning the runner to ubuntu-24.04 in this PR
helps the head side, but the internal_staging base is still recorded on
the old unpinned runner, so comparisons keep flapping until the pin
merges and the base is re-baselined.
Until that settles, the red X's on internal staging make the OSS
project look unhealthy and confuse contributors, so drop the
litellm_internal_staging push and pull_request triggers and keep
CodSpeed running on main only.
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Co-authored-by: mateo-berri <277851410+mateo-berri@users.noreply.github.com>