.Net: Update README.md (Typo "Azure Open AI"→"Azure OpenAI") (#11386)

https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Demos/VectorStoreRAG/README.md
#PingMSFTDocs

### Motivation and Context

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### Contribution Checklist

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Co-authored-by: Mark Wallace <[email protected]>

Author: hyoshioka0128

dotnet/samples/Demos/VectorStoreRAG/README.md

@@ -57,7 +57,7 @@ dotnet user-secrets set "AIServices:AzureOpenAI:Endpoint" "https://<yourservice>
 dotnet user-secrets set "AIServices:AzureOpenAI:ChatDeploymentName" "<your deployment name>"
 ```
 
-Note that the code doesn't use an API Key to communicate with Azure Open AI, but rather an `AzureCliCredential` so no api key secret is required.
+Note that the code doesn't use an API Key to communicate with Azure OpenAI, but rather an `AzureCliCredential` so no api key secret is required.
 
 ### OpenAI Chat Completion
 
@@ -83,7 +83,7 @@ dotnet user-secrets set "AIServices:AzureOpenAIEmbeddings:Endpoint" "https://<yo
 dotnet user-secrets set "AIServices:AzureOpenAIEmbeddings:DeploymentName" "<your deployment name>"
 ```
 
-Note that the code doesn't use an API Key to communicate with Azure Open AI, but rather an `AzureCliCredential` so no api key secret is required.
+Note that the code doesn't use an API Key to communicate with Azure OpenAI, but rather an `AzureCliCredential` so no api key secret is required.
 
 ### OpenAI Embeddings