Rollup merge of rust-lang#45118 - johnthagen:fix-section-key-name, r=alexcrichton

Fix variable name reference

As best I can tell, this was a typo due to how similar it looks to the function above it. PyCharm found this as a unbound local variable.

Author: kennytm

src/bootstrap/configure.py

@@ -378,7 +378,7 @@ def configure_section(lines, config):
 for section_key in config:
     section_config = config[section_key]
     if not section_key in sections:
-        raise RuntimeError("config key {} not in sections".format(key))
+        raise RuntimeError("config key {} not in sections".format(section_key))
 
     if section_key == 'target':
         for target in section_config: