[release] Prepare release core-1.13.1 (#6596)

Co-authored-by: opentelemetrybot <[email protected]>

Author: otelbot-dotnet[bot]

RELEASENOTES.md

@@ -4,6 +4,17 @@ This file contains highlights and announcements covering all components.
 For more details see `CHANGELOG.md` files maintained in the root source
 directory of each individual package.
 
+## 1.13.1
+
+Release details: [1.13.1](https://github.com/open-telemetry/opentelemetry-dotnet/releases/tag/core-1.13.1)
+
+* In version `1.13.0`, the digital signature (`.dll-keyless.sig`) and
+  certificate (`.dll-keyless.pem`) files were unintentionally omitted from the
+  published NuGet packages.
+* This hotfix restores the Sigstore signing artifacts for all target frameworks
+  (`net462`, `netstandard2.0`, `netstandard2.1`, `net8.0`, `net9.0`), ensuring
+  the integrity of DLL verification using Sigstore cosign.
+
 ## 1.13.0
 
 Release details: [1.13.0](https://github.com/open-telemetry/opentelemetry-dotnet/releases/tag/core-1.13.0)

src/OpenTelemetry.Api.ProviderBuilderExtensions/CHANGELOG.md

@@ -7,6 +7,10 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+## 1.13.1
+
+Released 2025-Oct-09
+
 ## 1.13.0
 
 Released 2025-Oct-01

src/OpenTelemetry.Api/CHANGELOG.md

@@ -6,6 +6,10 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+## 1.13.1
+
+Released 2025-Oct-09
+
 ## 1.13.0
 
 Released 2025-Oct-01

src/OpenTelemetry.Exporter.Console/CHANGELOG.md

@@ -6,6 +6,10 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+## 1.13.1
+
+Released 2025-Oct-09
+
 ## 1.13.0
 
 Released 2025-Oct-01

src/OpenTelemetry.Exporter.InMemory/CHANGELOG.md

@@ -6,6 +6,10 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+## 1.13.1
+
+Released 2025-Oct-09
+
 ## 1.13.0
 
 Released 2025-Oct-01

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/CHANGELOG.md

@@ -7,6 +7,10 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+## 1.13.1
+
+Released 2025-Oct-09
+
 ## 1.13.0
 
 Released 2025-Oct-01

src/OpenTelemetry.Exporter.Zipkin/CHANGELOG.md

@@ -6,6 +6,10 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+## 1.13.1
+
+Released 2025-Oct-09
+
 ## 1.13.0
 
 Released 2025-Oct-01

src/OpenTelemetry.Extensions.Hosting/CHANGELOG.md

@@ -6,6 +6,10 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+## 1.13.1
+
+Released 2025-Oct-09
+
 ## 1.13.0
 
 Released 2025-Oct-01

src/OpenTelemetry.Extensions.Propagators/CHANGELOG.md

@@ -6,6 +6,10 @@ covering all components see: [Release Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+## 1.13.1
+
+Released 2025-Oct-09
+
 ## 1.13.0
 
 Released 2025-Oct-01

src/OpenTelemetry/CHANGELOG.md

@@ -6,6 +6,10 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+## 1.13.1
+
+Released 2025-Oct-09
+
 * Fixed an issue where the Base2 Exponential Bucket Histogram did not reset its
   scale to 20 after each collection cycle when using delta aggregation temporality.
   ([#6557](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6557))