[ReleasePR containerinstance] ACI: Correct the type of httpHeaders object->array of object (#2392)

Create to sync Azure/azure-rest-api-specs#19103
[ReCreate this PR](https://github.com/azure-resource-manager-schemas/compare/main...azure-sdk:sdkAuto/containerinstance?expand=1)

Author: msftbot[bot]

schemas/2020-11-01/Microsoft.ContainerInstance.json

@@ -398,7 +398,10 @@
         "httpHeaders": {
           "oneOf": [
             {
-              "$ref": "#/definitions/HttpHeaders"
+              "type": "array",
+              "items": {
+                "$ref": "#/definitions/HttpHeader"
+              }
             },
             {
               "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
@@ -796,7 +799,7 @@
       ],
       "description": "The GPU resource."
     },
-    "HttpHeaders": {
+    "HttpHeader": {
       "type": "object",
       "properties": {
         "name": {
@@ -808,7 +811,7 @@
           "description": "The header value."
         }
       },
-      "description": "The HTTP headers."
+      "description": "The HTTP header."
     },
     "ImageRegistryCredential": {
       "type": "object",

schemas/2021-03-01/Microsoft.ContainerInstance.json

@@ -398,7 +398,10 @@
         "httpHeaders": {
           "oneOf": [
             {
-              "$ref": "#/definitions/HttpHeaders"
+              "type": "array",
+              "items": {
+                "$ref": "#/definitions/HttpHeader"
+              }
             },
             {
               "$ref": "https://schema.management.azure.com/schemas/common/definitions.json#/definitions/expression"
@@ -796,7 +799,7 @@
       ],
       "description": "The GPU resource."
     },
-    "HttpHeaders": {
+    "HttpHeader": {
       "type": "object",
       "properties": {
         "name": {
@@ -808,7 +811,7 @@
           "description": "The header value."
         }
       },
-      "description": "The HTTP headers."
+      "description": "The HTTP header"
     },
     "ImageRegistryCredential": {
       "type": "object",