fix read environment variable when backup or restoring db (#3615)

In some situations the reading of environment variables from the
container not works as expected with the `Invoke-ScriptInBcContainer`
cmdlt, f.i. the latest online sandbox (version 24.4.22295.23050) for
Italy on a self-hosted agent not returns any value, on an on-prem
sandbox (version 23 and also version 24) instead returns a value as
expected.

The following statement was launched on pwsh 7.4.2 with docker version
20.10.21, but returns no value:

```pwsh
Invoke-ScriptInBcContainer -containerName $containerName -scriptblock { $env:IsBcSandbox }
```

Using the following fix for this issue works as expected, and is much
more faster then invoking the script:

```pwsh
$inspect = docker inspect $containerName | ConvertFrom-Json
$inspect.Config.Env | Where-Object { $_ -eq "IsBcSandbox=Y" }
```

---------

Co-authored-by: Freddy Kristiansen <freddy.kristiansen@microsoft.com>

Bacpac/Backup-NavContainerDatabases.ps1

@@ -39,7 +39,9 @@ try {
     }
     elseif (!$bakFolder.Contains('\')) {
         $navversion = Get-BcContainerNavversion -containerOrImageName $containerName
-        if ((Invoke-ScriptInBcContainer -containerName $containerName -scriptblock { $env:IsBcSandbox }) -eq "Y") {
+        $inspect = docker inspect $containerName | ConvertFrom-Json
+        $isBcSandbox = $inspect.Config.Env | Where-Object { $_ -eq "IsBcSandbox=Y" }
+        if ($isBcSandbox) {
             $folderPrefix = "sandbox"
         }
         else {

Bacpac/Restore-DatabasesInNavContainer.ps1

@@ -59,7 +59,9 @@ try {
         }
         elseif (!$bakFolder.Contains('\')) {
             $navversion = Get-BcContainerNavversion -containerOrImageName $containerName
-            if ((Invoke-ScriptInBcContainer -containerName $containerName -scriptblock { $env:IsBcSandbox }) -eq "Y") {
+            $inspect = docker inspect $containerName | ConvertFrom-Json
+            $isBcSandbox = $inspect.Config.Env | Where-Object { $_ -eq "IsBcSandbox=Y" }
+            if ($isBcSandbox) {
                 $folderPrefix = "sandbox"
             }
             else {