Preserve quoted leading and trailing single-line whitespace

At least in a single line, whitespace in a double-quoted value in a
configuration file, like `name = " abc def "`, would presumably be
intended. This removes the `strip()` call that is applied to text
`ConfigParser` obtained by removing the double quotes around it.

This slightly refines the changes in #2035 by dropping the `strip()`
call while continuing to remove opening and closing double quotes.

Author: EliahKagan

git/config.py

@@ -509,7 +509,7 @@ def string_decode(v: str) -> str:
                         is_multi_line = True
                         optval = string_decode(optval[1:])
                     elif len(optval) > 1 and optval[0] == '"' and optval[-1] == '"':
-                        optval = optval[1:-1].strip()
+                        optval = optval[1:-1]
                     # END handle multi-line
                     # Preserves multiple values for duplicate optnames.
                     cursect.add(optname, optval)