Add Python to placeholder pool list (#7600)

Author: pgombar

src/WebJobs.Script/Workers/Rpc/RpcInitializationService.cs

@@ -49,7 +49,8 @@ public class RpcInitializationService : IManagedHostedService
         {
             RpcWorkerConstants.JavaLanguageWorkerName,
             RpcWorkerConstants.NodeLanguageWorkerName,
-            RpcWorkerConstants.PowerShellLanguageWorkerName
+            RpcWorkerConstants.PowerShellLanguageWorkerName,
+            RpcWorkerConstants.PythonLanguageWorkerName
         };
 
         public RpcInitializationService(IOptionsMonitor<ScriptApplicationHostOptions> applicationHostOptions, IEnvironment environment, IRpcServer rpcServer, IWebHostRpcWorkerChannelManager rpcWorkerChannelManager, ILogger<RpcInitializationService> logger)

test/WebJobs.Script.Tests/Workers/Rpc/RpcInitializationServiceTests.cs

@@ -326,7 +326,8 @@ public void ShouldStartStandbyPlaceholderChannels_Returns_ExpectedValue(string p
         [InlineData("1", "java", "", true)]
         [InlineData("1", "", "1234", false)]
         [InlineData("1", "dotnet", "1234", false)]
-        [InlineData("1", "python", "1234", false)]
+        [InlineData("1", "python", "1234", true)]
+        [InlineData("0", "python", "1234", false)]
         public void ShouldStartAsPlaceholderPool_Returns_ExpectedValue(string placeholderMode, string workerRuntime, string siteInstanaceId, bool expectedResult)
         {
             Mock<IRpcServer> testRpcServer = new Mock<IRpcServer>();