Upgrade the used otlp version in readme (open-telemetry#10167)

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Ex. Adding a feature - Explain what this achieves.-->
#### Description

We upgraded the proto version, so we need to upgrade it in the readme as
well.

<!-- Issue number if applicable -->
#### Link to tracking issue

*
open-telemetry#10109 (review)
* open-telemetry#10155

README.md

@@ -24,7 +24,7 @@
     <img alt="GitHub release (latest by date including pre-releases)" src="https://img.shields.io/github/v/release/open-telemetry/opentelemetry-collector?include_prereleases&style=for-the-badge">
   </a>
   <a href="https://www.bestpractices.dev/projects/8404"><img src="https://www.bestpractices.dev/projects/8404/badge">
-  </a> 
+  </a>
 </p>
 
 <p align="center">
@@ -61,7 +61,7 @@ Objectives:
 
 ## Supported OTLP version
 
-This code base is currently built against using OTLP protocol v1.1.0,
+This code base is currently built against using OTLP protocol v1.3.1,
 considered Stable. [See the OpenTelemetry Protocol Stability
 definition
 here.](https://github.com/open-telemetry/opentelemetry-proto?tab=readme-ov-file#stability-definition)