chore(vcs): rewrite git config update to not sync on each change

The set_value interface immediatelly writes out any change making our
batching ineffective. Sticking to native ConfigParser set interface
makes it write the file when leaving the context. This also needs we
need to manually create missing sections.

weblate/vcs/git.py

@@ -153,10 +153,13 @@ def git_config_update(
                         continue
                     if old == value:
                         continue
-                except (NoSectionError, NoOptionError):
+                except NoSectionError:
+                    if value is not None:
+                        config.add_section(section)
+                except NoOptionError:
                     pass
                 if value is not None:
-                    config.set_value(section, key, value)
+                    config.set(section, key, value)
 
     def config_update(self, *updates: tuple[str, str, str | None]) -> None:
         filename = Path(self.path) / ".git" / "config"