Fix typos in gc.c and gc.rb

Author: hi

gc.c

@@ -1816,7 +1816,7 @@ id2ref_tbl_mark(void *data)
         // It's very unlikely, but if enough object ids were generated, keys may be T_BIGNUM
         rb_mark_set(table);
     }
-    // We purposedly don't mark values, as they are weak references.
+    // We purposely don't mark values, as they are weak references.
     // rb_gc_obj_free_vm_weak_references takes care of cleaning them up.
 }
 

gc.rb

@@ -37,7 +37,7 @@ module GC
   #     interleaved with program execution both before the method returns and afterward;
   #     therefore sweeping may not be completed before the return.
   #
-  # Note that these keword arguments are implementation- and version-dependent,
+  # Note that these keyword arguments are implementation- and version-dependent,
   # are not guaranteed to be future-compatible,
   # and may be ignored in some implementations.
   def self.start full_mark: true, immediate_mark: true, immediate_sweep: true