bump version (#2620)

Author: Timothy Mothra

.props/_GlobalStaticVersion.props

@@ -13,7 +13,7 @@
     <SemanticVersionMajor>2</SemanticVersionMajor>
     <SemanticVersionMinor>21</SemanticVersionMinor> <!-- If changing the Minor version, also update the Date value. -->
     <SemanticVersionPatch>0</SemanticVersionPatch>
-    <PreReleaseMilestone>beta2</PreReleaseMilestone> <!--Valid values: beta1, beta2, EMPTY for stable -->
+    <PreReleaseMilestone>beta3</PreReleaseMilestone> <!--Valid values: beta1, beta2, EMPTY for stable -->
     <PreReleaseMilestone Condition="'$(Redfield)' == 'True'">redfield</PreReleaseMilestone>
     <PreReleaseMilestone Condition="'$(NightlyBuild)' == 'True'">nightly</PreReleaseMilestone> <!-- Overwrite this property for nightly builds from the DEVELOP branch. -->
     <!-- 

CHANGELOG.md

@@ -1,6 +1,8 @@
 # Changelog
 
 ## VNext
+
+## Version 2.21.0-beta3
 - [Remove two unnecessary .NET Standard 1.x dependencies.](https://github.com/microsoft/ApplicationInsights-dotnet/pull/2613)
 - Address vulnerability in `Newtonsoft.Json` ([GHSA-5crp-9r3c-p9vr](https://github.com/advisories/GHSA-5crp-9r3c-p9vr)). 
   Mitigation is to upgrade dependencies in `Microsoft.ApplicationInsights.AspNetCore` ([#2615](https://github.com/microsoft/ApplicationInsights-dotnet/pull/2615))