Remove pre-release OpenTelemetry pins from generated constraints

Our generated constraints currently pin two packages to pre-release (beta) versions: ``` opentelemetry-exporter-prometheus==0.65b0 opentelemetry-semantic-conventions==0.65b0 ``` These are the only pre-releases in the constraints files we tag and ship, and both require a hardcoded exception in [`scripts/in_container/run_generate_constraints.py`](https://github.com/apache/airflow/blob/main/scripts/in_container/run_generate_constraints.py) (`additional_constraints_for_highest_resolution`). ### Why the exception exists Constraints cut for a release candidate resolve with `--prerelease explicit`, which permits a pre-release only for packages some requirement explicitly marks as such, and drops the `if-necessary` fallback. Neither OpenTelemetry package has *ever* published a final release - every version on PyPI is `0.NNbM` (61 releases for `opentelemetry-semantic-conventions`, 55 for `opentelemetry-exporter-prometheus`, zero non-pre-release among them). Without an explicit pre-release lower bound in the resolution, they cannot resolve at all and constraints generation fails with `No solution found`. ### Where they come from - `opentelemetry-exporter-prometheus` - direct dependency of the `otel` extra of `apache-airflow-core` (which is part of the `all` extra), `>=0.47b0`. - `opentelemetry-semantic-conventions` - hard transitive dependency of `opentelemetry-sdk`, which comes in via `opentelemetry-exporter-otlp` (a core `apache-airflow-core` dependency) and directly via `shared/observability` and `shared/listeners`. So neither pin can simply be dropped today: `semantic-conventions` is unavoidable as long as we depend on the OpenTelemetry SDK at all. ### What needs to happen Any of the following would let us delete the exception: 1. **Upstream stabilisation** - OpenTelemetry Python graduates these components to `1.x` finals. This is the real fix and is outside our control; it needs tracking against [`open-telemetry/opentelemetry-python`](https://github.com/open-telemetry/op…