Preserve formatting with tomlkit

.github/workflows/update_backend.yml

@@ -20,7 +20,7 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install -r requirements.txt
-          pip install toml json
+          pip install tomlkit
           pip install .
           python -c 'import pysr'
 

.github/workflows/update_backend_version.py

@@ -2,15 +2,15 @@
 import sys
 from pathlib import Path
 
-import toml
+import tomlkit
 
 new_backend_version = sys.argv[1]
 
 pyproject_toml = Path(__file__).parent / ".." / ".." / "pyproject.toml"
 juliapkg_json = Path(__file__).parent / ".." / ".." / "pysr" / "juliapkg.json"
 
 with open(pyproject_toml) as toml_file:
-    pyproject_data = toml.load(toml_file)
+    pyproject_data = tomlkit.parse(toml_file.read())
 
 with open(juliapkg_json) as f:
     juliapkg_data = json.load(f)
@@ -21,7 +21,7 @@
 juliapkg_data["packages"]["SymbolicRegression"]["version"] = f"={new_backend_version}"
 
 with open(pyproject_toml, "w") as toml_file:
-    toml.dump(pyproject_data, toml_file)
+    toml_file.write(tomlkit.dumps(pyproject_data))
 
 with open(juliapkg_json, "w") as f:
     json.dump(juliapkg_data, f, indent=4)