docs: fix indent of builtins and nix.conf descriptions in manual

The manual for the builtins and nix.conf currently has inconsistent
indentation, which causes some of the descriptions to end up being
partially treatedas code blocks in markdown (and thus the manual).

This was simply caused by the template string for the docs having
too much indentation before the description is inserted, so this fixes
that 16-bytes mistake.

Change-Id: Ia264e3b1abb20430109029d07a2d2b0a1a726bd4

lix/code-generation/build_builtins.py

@@ -52,7 +52,7 @@ class Builtin:
             </dt>
             <dd>
 
-            {indent(self.documentation, "    " * 3)}
+{indent(self.documentation, "    " * 3)}
 
             {
             f"This function is only available if the [{self.experimental_feature}](@docroot@/contributing/experimental-features.md#xp-feature-{self.experimental_feature}) experimental feature is enabled."

lix/code-generation/build_settings.py

@@ -90,7 +90,7 @@ class Setting:
         aliases = [f"`{item}`" for item in self.aliases]
         description = dedent(f"""
 
-            {indent(indentation, self.documentation)}
+{indent(indentation, self.documentation)}
 
             {indent(indentation, PLATFORM_WARNING.format(platforms=str(platforms)[1:-1])) if self.platforms else ""}
             {indent(indentation, XP_WARNING.format(feature=self.experimental_feature, name=self.name)) if self.experimental_feature is not None else ""}