Improve Run-Tests.ps1's maintainability and readability (#15407)

Improvements and explanations:
* Added proper indentation and spacing for better readability.
* Added comments to explain the purpose of different sections of the
  code.
* Utilized the $LASTEXITCODE variable instead of $lastexitcode to ensure
  consistency.
* Changed the variable name from $testdlls to $testDlls for better
  naming convention.
* Moved the Exit 0 statement to the end (outside the if condition).
* Since Exit statements terminate the script immediately, it's better to
  have them at the end of the script to ensure that all necessary
  cleanup or additional operations are performed before exiting.
* These improvements enhance the code's readability, maintainability,
  and adherence to best practices.

.github/actions/spelling/expect/expect.txt

@@ -986,6 +986,7 @@ KVM
 langid
 LANGUAGELIST
 lasterror
+LASTEXITCODE
 lastexitcode
 LAYOUTRTL
 lbl

build/scripts/Run-Tests.ps1

@@ -1,27 +1,36 @@
 [CmdLetBinding()]
 Param(
-    [Parameter(Mandatory=$true, Position=0)][string]$MatchPattern,
-    [Parameter(Mandatory=$true, Position=1)][string]$Platform,
-    [Parameter(Mandatory=$true, Position=2)][string]$Configuration,
-    [Parameter(Mandatory=$false, Position=3)][string]$LogPath,
-    [Parameter(Mandatory=$false)][string]$Root = ".\bin\$Platform\$Configuration"
+    [Parameter(Mandatory=$true, Position=0)]
+    [string]$MatchPattern,
+    [Parameter(Mandatory=$true, Position=1)]
+    [string]$Platform,
+    [Parameter(Mandatory=$true, Position=2)]
+    [string]$Configuration,
+    [Parameter(Mandatory=$false, Position=3)]
+    [string]$LogPath,
+    [Parameter(Mandatory=$false)]
+    [string]$Root = ".\bin\$Platform\$Configuration"
 )
 
-$testdlls = Get-ChildItem -Path "$Root" -Recurse -Filter $MatchPattern
+# Find test DLLs based on the provided root, match pattern, and recursion
+$testDlls = Get-ChildItem -Path $Root -Recurse -Filter $MatchPattern
 
+$args = @()
 
-$args = @();
-
-if ($LogPath)
-{
-    $args += '/enablewttlogging';
-    $args += '/appendwttlogging';
-    $args += "/logFile:$LogPath";
-    Write-Host "Wtt Logging Enabled";
+# Check if the LogPath parameter is provided and enable WTT logging
+if ($LogPath) {
+    $args += '/enablewttlogging'
+    $args += '/appendwttlogging'
+    $args += "/logFile:$LogPath"
+    Write-Host "WTT Logging Enabled"
 }
 
-&"$Root\te.exe" $args $testdlls.FullName
+# Invoke the te.exe executable with arguments and test DLLs
+& "$Root\te.exe" $args $testDlls.FullName
 
-if ($lastexitcode -Ne 0) { Exit $lastexitcode }
+# Check the exit code of the te.exe process and exit accordingly
+if ($LASTEXITCODE -ne 0) {
+    Exit $LASTEXITCODE
+}
 
 Exit 0