Fix links broken by branch rename (#22416)

Correct links broken during the master->main branch rename

sdk/identity/azure-identity/README.md

@@ -50,7 +50,7 @@ The `DefaultAzureCredential` is appropriate for most scenarios where the applica
 
  The `DefaultAzureCredential` will attempt to authenticate via the following mechanisms in order.
 
-![DefaultAzureCredential authentication flow](https://github.com/Azure/azure-sdk-for-java/raw/master/sdk/identity/azure-identity/images/defaultazurecredential.png)
+![DefaultAzureCredential authentication flow](https://github.com/Azure/azure-sdk-for-java/raw/main/sdk/identity/azure-identity/images/defaultazurecredential.png)
 
  - Environment - The `DefaultAzureCredential` will read account information specified via [environment variables](#environment-variables) and use it to authenticate.
  - Managed Identity - If the application is deployed to an Azure host with Managed Identity enabled, the `DefaultAzureCredential` will authenticate with that account.
@@ -62,7 +62,7 @@ The `DefaultAzureCredential` is appropriate for most scenarios where the applica
 You can find more examples of using various credentials in [Azure Identity Examples Wiki page](https://github.com/Azure/azure-sdk-for-java/wiki/Azure-Identity-Examples). 
 
 ### Authenticating with `DefaultAzureCredential`
-This example demonstrates authenticating the `SecretClient` from the [azure-security-keyvault-secrets][secrets_client_library] client library using the `DefaultAzureCredential`. There's also [a compilable sample](https://github.com/Azure/azure-sdk-for-java/tree/master/sdk/keyvault/azure-security-keyvault-secrets/src/samples/java/com/azure/security/keyvault/secrets/IdentityReadmeSamples.java) to create a Key Vault secret client you can copy-paste.
+This example demonstrates authenticating the `SecretClient` from the [azure-security-keyvault-secrets][secrets_client_library] client library using the `DefaultAzureCredential`. There's also [a compilable sample](https://github.com/Azure/azure-sdk-for-java/tree/main/sdk/keyvault/azure-security-keyvault-secrets/src/samples/java/com/azure/security/keyvault/secrets/IdentityReadmeSamples.java) to create a Key Vault secret client you can copy-paste.
 
 <!-- embedme ../../keyvault/azure-security-keyvault-secrets/src/samples/java/com/azure/security/keyvault/secrets/IdentityReadmeSamples.java#L40-L52 -->
 ```java
@@ -443,14 +443,14 @@ This project has adopted the [Microsoft Open Source Code of Conduct][code_of_con
 <!-- LINKS -->
 [azure_cli]: https://docs.microsoft.com/cli/azure
 [azure_sub]: https://azure.microsoft.com/free/
-[source]: https://github.com/Azure/azure-sdk-for-java/tree/master/sdk/identity/azure-identity
+[source]: https://github.com/Azure/azure-sdk-for-java/tree/main/sdk/identity/azure-identity
 [aad_doc]: https://docs.microsoft.com/azure/active-directory/
 [code_of_conduct]: https://opensource.microsoft.com/codeofconduct/
-[keys_client_library]: https://github.com/Azure/azure-sdk-for-java/tree/master/sdk/keyvault/azure-security-keyvault-keys
+[keys_client_library]: https://github.com/Azure/azure-sdk-for-java/tree/main/sdk/keyvault/azure-security-keyvault-keys
 [logging]: https://github.com/Azure/azure-sdk-for-java/wiki/Logging-with-Azure-SDK
-[secrets_client_library]: https://github.com/Azure/azure-sdk-for-java/tree/master/sdk/keyvault/azure-security-keyvault-secrets
-[eventhubs_client_library]: https://github.com/Azure/azure-sdk-for-java/tree/master/sdk/eventhubs/azure-messaging-eventhubs
-[azure_core_library]: https://github.com/Azure/azure-sdk-for-java/tree/master/sdk/core
+[secrets_client_library]: https://github.com/Azure/azure-sdk-for-java/tree/main/sdk/keyvault/azure-security-keyvault-secrets
+[eventhubs_client_library]: https://github.com/Azure/azure-sdk-for-java/tree/main/sdk/eventhubs/azure-messaging-eventhubs
+[azure_core_library]: https://github.com/Azure/azure-sdk-for-java/tree/main/sdk/core
 [javadoc]: https://azure.github.io/azure-sdk-for-java
 [jdk_link]: https://docs.microsoft.com/java/azure/jdk/?view=azure-java-stable