Stop generating header filenames with a newline in them

generate-app-headers.sh read APP with a plain grep -oP, so a script that
sets APP twice yielded both lines and the filename became
"almalinux
almalinux${var_version}vm". Three of those are in the tree
and they make main impossible to check out on Windows.

Nothing reads vm/headers: get_header fetches banners from the core
repo, which already carries clean almalinux, debian and ubuntu.

.github/workflows/scripts/generate-app-headers.sh

@@ -22,7 +22,9 @@ generate_headers() {
   for script in "${file_list[@]}"; do
     [[ -f "$script" ]] || continue
 
-    app_name=$(grep -oP '^APP="\K[^"]+' "$script" 2>/dev/null)
+    # -m1: a script that sets APP twice (the second carrying ${var_version})
+    # otherwise yields both lines, and the filename gets a newline in it.
+    app_name=$(grep -m1 -oP '^APP="\K[^"]+' "$script" 2>/dev/null)
     if [[ -n "$app_name" ]]; then
       # core.func/vm-core.func look the header up as "${APP,,}" without spaces,
       # so the generated file has to be named after APP - not after the script.

vm/headers/almalinux almalinux${var_version}vm

@@ -1,12 +0,0 @@
-    ___    __                __    _                 
-   /   |  / /___ ___  ____ _/ /   (_)___  __  ___  __
-  / /| | / / __ `__ \/ __ `/ /   / / __ \/ / / / |/_/
- / ___ |/ / / / / / / /_/ / /___/ / / / / /_/ />  <  
-/_/  |_/_/_/ /_/ /_/\__,_/_____/_/_/ /_/\__,_/_/|_|  
-                                                     
-    ___    __                __    _                      __   __                                      _             _      _    ____  ___
-   /   |  / /___ ___  ____ _/ /   (_)___  __  ___  __   _/ / _/_/   ______ _______   _____  __________(_)___  ____  | |    | |  / /  |/  /
-  / /| | / / __ `__ \/ __ `/ /   / / __ \/ / / / |/_/  / __//_/| | / / __ `/ ___/ | / / _ \/ ___/ ___/ / __ \/ __ \ / /    | | / / /|_/ / 
- / ___ |/ / / / / / / /_/ / /___/ / / / / /_/ />  <   (_  < <  | |/ / /_/ / /   | |/ /  __/ /  (__  ) / /_/ / / / /_>_>    | |/ / /  / /  
-/_/  |_/_/_/ /_/ /_/\__,_/_____/_/_/ /_/\__,_/_/|_|  /  _// /  |___/\__,_/_/____|___/\___/_/  /____/_/\____/_/ /_//_/      |___/_/  /_/   
-                                                     /_/  \_\             /_____/                               /_/                       

vm/headers/debian debian${var_version}

@@ -1,12 +0,0 @@
-    ____       __    _           
-   / __ \___  / /_  (_)___ _____ 
-  / / / / _ \/ __ \/ / __ `/ __ \
- / /_/ /  __/ /_/ / / /_/ / / / /
-/_____/\___/_.___/_/\__,_/_/ /_/ 
-                                 
-    ____       __    _                 __   __                                      _             _ 
-   / __ \___  / /_  (_)___ _____     _/ / _/_/   ______ _______   _____  __________(_)___  ____  | |
-  / / / / _ \/ __ \/ / __ `/ __ \   / __//_/| | / / __ `/ ___/ | / / _ \/ ___/ ___/ / __ \/ __ \ / /
- / /_/ /  __/ /_/ / / /_/ / / / /  (_  < <  | |/ / /_/ / /   | |/ /  __/ /  (__  ) / /_/ / / / /_>_>
-/_____/\___/_.___/_/\__,_/_/ /_/  /  _// /  |___/\__,_/_/____|___/\___/_/  /____/_/\____/_/ /_//_/  
-                                  /_/  \_\             /_____/                               /_/    

vm/headers/ubuntu ubuntu${var_version}vm

@@ -1,12 +0,0 @@
-   __  ____                __       
-  / / / / /_  __  ______  / /___  __
- / / / / __ \/ / / / __ \/ __/ / / /
-/ /_/ / /_/ / /_/ / / / / /_/ /_/ / 
-\____/_.___/\__,_/_/ /_/\__/\__,_/  
-                                    
-   __  ____                __            __   __                                      _             _      _    ____  ___
-  / / / / /_  __  ______  / /___  __   _/ / _/_/   ______ _______   _____  __________(_)___  ____  | |    | |  / /  |/  /
- / / / / __ \/ / / / __ \/ __/ / / /  / __//_/| | / / __ `/ ___/ | / / _ \/ ___/ ___/ / __ \/ __ \ / /    | | / / /|_/ / 
-/ /_/ / /_/ / /_/ / / / / /_/ /_/ /  (_  < <  | |/ / /_/ / /   | |/ /  __/ /  (__  ) / /_/ / / / /_>_>    | |/ / /  / /  
-\____/_.___/\__,_/_/ /_/\__/\__,_/  /  _// /  |___/\__,_/_/____|___/\___/_/  /____/_/\____/_/ /_//_/      |___/_/  /_/   
-                                    /_/  \_\             /_____/                               /_/