fix: Fixes website slot Private Endpoint configuration (Azure#926)

## Description

Closes Azure#925 

## Pipeline


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Co-authored-by: ChrisSidebotham-MSFT <48600046+ChrisSidebotham@users.noreply.github.com>
Co-authored-by: Buddy <38195643+tsc-buddy@users.noreply.github.com>

avm/res/web/site/main.bicep

@@ -275,7 +275,7 @@ module app_slots 'slot/main.bicep' = [for (slot, index) in (slots ?? []): {
     appSettingsKeyValuePairs: slot.?appSettingsKeyValuePairs ?? appSettingsKeyValuePairs
     basicPublishingCredentialsPolicies: slot.?basicPublishingCredentialsPolicies ?? basicPublishingCredentialsPolicies
     lock: slot.?lock ?? lock
-    privateEndpoints: slot.?privateEndpoints ?? privateEndpoints
+    privateEndpoints: slot.?privateEndpoints ?? []
     tags: slot.?tags ?? tags
     clientCertEnabled: slot.?clientCertEnabled
     clientCertExclusionPaths: slot.?clientCertExclusionPaths

avm/res/web/site/main.json

@@ -6,7 +6,7 @@
     "_generator": {
       "name": "bicep",
       "version": "0.24.24.22086",
-      "templateHash": "6827854649814438473"
+      "templateHash": "10377090959004552073"
     },
     "name": "Web/Function Apps",
     "description": "This module deploys a Web or Function App.",
@@ -1191,7 +1191,7 @@
             "value": "[coalesce(tryGet(coalesce(parameters('slots'), createArray())[copyIndex()], 'lock'), parameters('lock'))]"
           },
           "privateEndpoints": {
-            "value": "[coalesce(tryGet(coalesce(parameters('slots'), createArray())[copyIndex()], 'privateEndpoints'), parameters('privateEndpoints'))]"
+            "value": "[coalesce(tryGet(coalesce(parameters('slots'), createArray())[copyIndex()], 'privateEndpoints'), createArray())]"
           },
           "tags": {
             "value": "[coalesce(tryGet(coalesce(parameters('slots'), createArray())[copyIndex()], 'tags'), parameters('tags'))]"