fix: use apt-get instead of apt

src/SPC/doctor/item/LinuxMuslCheck.php

@@ -37,7 +37,7 @@ class LinuxMuslCheck
     public function fixMusl(array $distro): bool
     {
         $install_cmd = match ($distro['dist']) {
-            'ubuntu', 'debian' => 'apt install musl musl-tools -y',
+            'ubuntu', 'debian' => 'apt-get install musl musl-tools -y',
             'alpine' => 'apk add musl musl-utils musl-dev',
             default => throw new RuntimeException('Current linux distro is not supported for auto-install musl packages'),
         };

src/SPC/doctor/item/LinuxToolCheckList.php

@@ -77,7 +77,7 @@ class LinuxToolCheckList
     public function fixBuildTools(array $distro, array $missing): bool
     {
         $install_cmd = match ($distro['dist']) {
-            'ubuntu', 'debian' => 'apt install -y',
+            'ubuntu', 'debian' => 'apt-get install -y',
             'alpine' => 'apk add',
             default => throw new RuntimeException('Current linux distro is not supported for auto-install musl packages'),
         };

src/SPC/store/Downloader.php

@@ -253,6 +253,12 @@ class Downloader
             $source = Config::getSource($name);
         }
 
+        if ($source === null) {
+            logger()->warning('Source {name} unknown. Skipping.', ['name' => $name]);
+
+            return;
+        }
+
         // load lock file
         if (!file_exists(DOWNLOAD_PATH . '/.lock.json')) {
             $lock = [];