runtests: include missing valgrind package

use valgrind was missing which caused torture tests with valgrind
enabled to fail.

Reported-by: Daniel Stenberg
Fixes #11364
Closes #11365

tests/runner.pm

@@ -105,6 +105,7 @@ use testutil qw(
     subbase64
     subnewlines
     );
+use valgrind;
 
 
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