[Tests] NFC: Mark one of the fuzzer crashers as fixed

Author: xedin

validation-test/compiler_crashers_2/fa3981f71bc0d522.swift renamed to validation-test/compiler_crashers_2_fixed/fa3981f71bc0d522.swift

@@ -1,3 +1,3 @@
 // {"signature":"(anonymous namespace)::ExprWalker::rewriteTarget(swift::constraints::SyntacticElementTarget)"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 {                   Sendable(Sendable<<a