Run opentelemetry-jaeger tests consecutively (#1384)

Limit threads to 1 (to force tests to run
consecutively) to temporarily fix random [failures](https://github.com/open-telemetry/opentelemetry-rust/actions/runs/6915742069/job/18815025248)
during `opentelemetry-jaeger` tests, due to environment variable updates
from parallel tests
If you run this command line multiple times, you should be able to
reproduce it (`test_resolve_timeout` and `test_resolve_endpoint` are
updating some environment variables)
```shell
cargo test --manifest-path=opentelemetry-jaeger/Cargo.toml --all-features collector -- --test-threads=5
```

Author: harscoet

scripts/test.sh

@@ -11,6 +11,6 @@ cargo test --manifest-path=opentelemetry/Cargo.toml --no-default-features
 cargo test --manifest-path=opentelemetry/Cargo.toml --all-features -- --ignored --test-threads=1
 
 cargo test --manifest-path=opentelemetry/Cargo.toml --all-features
-cargo test --manifest-path=opentelemetry-jaeger/Cargo.toml --all-features
+cargo test --manifest-path=opentelemetry-jaeger/Cargo.toml --all-features -- --test-threads=1
 cargo test --manifest-path=opentelemetry-otlp/Cargo.toml --features "trace,grpc-sys" --no-default-features
 cargo test --manifest-path=opentelemetry-zipkin/Cargo.toml --all-features