dialects: (llvm) avoid double whitespace after exact (#3415)

The pretty printer of the `exact` keyword accidentally printed two
whitespaces in a row, which led to non-canical code being emitted. This
change ensures we only print a single whitespace after the `exact`
keyword.

xdsl/dialects/llvm.py

@@ -509,7 +509,7 @@ def parse_exact(cls, parser: Parser):
 
     def print_exact(self, printer: Printer) -> None:
         if self.is_exact:
-            printer.print(" exact ")
+            printer.print(" exact")
 
     @classmethod
     def parse(cls, parser: Parser):