Update opentelemetry-exporter-otlp requirement from >= 0.25, < 0.28 t…

…o >= 0.25, < 0.29

Updates the requirements on [opentelemetry-exporter-otlp](https://github.com/open-telemetry/opentelemetry-ruby) to permit the latest version.
- [Release notes](https://github.com/open-telemetry/opentelemetry-ruby/releases)
- [Changelog](https://github.com/open-telemetry/opentelemetry-ruby/blob/main/exporter/otlp/CHANGELOG.md)
- [Commits](open-telemetry/opentelemetry-ruby@opentelemetry-exporter-otlp/v0.25.0...opentelemetry-exporter-otlp/v0.28.0)

---
updated-dependencies:
- dependency-name: opentelemetry-exporter-otlp
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

govuk_app_config.gemspec

@@ -21,7 +21,7 @@ Gem::Specification.new do |spec|
   spec.require_paths = %w[lib]
 
   spec.add_dependency "logstasher", "~> 2.1"
-  spec.add_dependency "opentelemetry-exporter-otlp", ">= 0.25", "< 0.28"
+  spec.add_dependency "opentelemetry-exporter-otlp", ">= 0.25", "< 0.29"
   spec.add_dependency "opentelemetry-instrumentation-all", ">= 0.39.1", "< 0.62.0"
   spec.add_dependency "opentelemetry-sdk", "~> 1.2"
   spec.add_dependency "plek", ">= 4", "< 6"