[chore] Fix Slack badge in README.md (#3059)

Author: arminru

README.md

@@ -3,7 +3,7 @@
 [![Checks](https://github.com/open-telemetry/semantic-conventions/workflows/Checks/badge.svg)](https://github.com/open-telemetry/semantic-conventions/actions?query=workflow%3A%22Checks%22+branch%3Amain)
 [![GitHub tag (latest SemVer)](https://img.shields.io/github/tag/open-telemetry/semantic-conventions.svg?logo=opentelemetry&&color=f5a800&label=Latest%20release)](https://github.com/open-telemetry/semantic-conventions/releases/latest)
 [![Specification Version](https://img.shields.io/badge/OTel_specification_version-v1.50.0-blue?logo=opentelemetry&color=f5a800)](https://github.com/open-telemetry/opentelemetry-specification/releases/tag/v1.50.0)
-[![Slack](https://img.shields.io/badge/Slack-otel_semantic_conventions-purple)](https://cloud-native.slack.com/archives/C041APFBYQP)
+[![Slack](https://img.shields.io/badge/Slack-%23otel--semantic--conventions-purple)](https://cloud-native.slack.com/archives/C041APFBYQP)
 
 Semantic Conventions define a common set of (semantic) attributes which
 provide meaning to data when collecting, producing and consuming it.