Update Lean.sublime-syntax from Lean 3 to Lean 4

Resolves #3286

1. `lean4.json` → `lean4.tmLanguage`

    1. Download `vscode-lean4/syntaxes/lean4.json` from https://github.com/leanprover/vscode-lean4/pull/623 (now merged).
    2. Install the VS Code extension [TextMate Languages (pedro-w)](https://marketplace.visualstudio.com/items?itemName=pedro-w.tmlanguage).
    3. Open `lean4.json` in VS Code, <kbd>F1</kbd>, and “Convert to tmLanguage PLIST File”.

2. `lean4.tmLanguage` → `lean4.sublime-syntax`

    Open `lean4.tmLanguage` in Sublime text, “Tools → Developer → New Syntax from lean4.tmLanguage…”.

.gitmodules

@@ -196,7 +196,7 @@
 	branch = bat-source
 [submodule "assets/syntaxes/02_Extra/Lean"]
 	path = assets/syntaxes/02_Extra/Lean
-	url = https://github.com/leanprover/vscode-lean.git
+	url = https://github.com/leanprover/vscode-lean4.git
 [submodule "assets/syntaxes/02_Extra/Zig"]
 	path = assets/syntaxes/02_Extra/Zig
 	url = https://github.com/ziglang/sublime-zig-language.git