Lint: fix issues with unnecessary wraps

[ozerovandrei]

Remove Result from return types in tests of opentelemetry-datadog,
opentelemetry-jaeger, opentelemetry-otlp, opentelemetry-zipkin.

Reference: rust-lang/rust-clippy#6070

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@238e797). Click here to learn what that means.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #456   +/-   ##
=======================================
  Coverage        ?   47.88%           
=======================================
  Files           ?       95           
  Lines           ?     8736           
  Branches        ?        0           
=======================================
  Hits            ?     4183           
  Misses          ?     4553           
  Partials        ?        0           

Impacted Files	Coverage Δ
opentelemetry-datadog/src/exporter/mod.rs	14.45% <100.00%> (ø)
opentelemetry-jaeger/src/exporter/mod.rs	40.31% <100.00%> (ø)
opentelemetry-zipkin/src/exporter/model/span.rs	94.25% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 238e797...11d75a4. Read the comment docs.

[jtescher]

Looks good, thanks