This is a fix to set the field value before Validate()

[pjuarezd]

Validate() verifies the field JWTSupplier is not null before its assigned, causing a Parameter 'JWTSupplier JWT Token supplier cannot be null.' exception.

Breakins IAMAWSProvider.GetAccessCredentials

minio-dotnet/Minio/Credentials/IAMAWSProvider.cs

Lines 93 to 103 in b332b78

	ClientProvider provider = new WebIdentityProvider()
	.WithJWTSupplier(() =>
	{
	var tokenContents = File.ReadAllText(tokenFile);
	return new JsonWebToken(tokenContents, 0);
	})
	.WithSTSEndpoint(url)
	.WithDurationInSeconds(null)
	.WithPolicy(null)
	.WithRoleARN(Environment.GetEnvironmentVariable("AWS_ROLE_ARN"))
	.WithRoleSessionName(Environment.GetEnvironmentVariable("AWS_ROLE_SESSION_NAME"));

This is a fix to set the field value before Validate().