Fix syntax of the build script

Author: 0x5bfa

.github/scripts/Build-AppSolution.ps1

@@ -3,13 +3,13 @@
 
 param(
     [string]$ReleaseBranch =            "Debug", # This has to correspond with one of the AppEnvironment enum values
-    [string]$SolutionPath =             "Files.slnx"
-    [string]$StartupProjectPath =       ""
-    [string]$Platform =                 "x64"
-    [string]$Configuration =            "Debug"
-    [string]$AppxBundlePlatforms =      "x64|arm64"
-    [string]$AppxPackageDir =           ""
-    [string]$AppInstallerUrl =          "" # Sideload only
+    [string]$SolutionPath =             "Files.slnx",
+    [string]$StartupProjectPath =       "",
+    [string]$Platform =                 "x64",
+    [string]$Configuration =            "Debug",
+    [string]$AppxBundlePlatforms =      "x64|arm64",
+    [string]$AppxPackageDir =           "",
+    [string]$AppInstallerUrl =          "", # Sideload only
     [string]$AppxPackageCertKeyFile =   "" # Debug only
 )