[scudo/standalone] Fix undefined behavior in checksum test

1U has type unsigned int, and << of 32 or more is undefined behavior.
Use the proper type in the lhs of the shift.

Reviewed By: cryptoad

Differential Revision: https://reviews.llvm.org/D87973

GitOrigin-RevId: f5fa5b9fe3b02f26b38612f96cba19aceccbc2a3
diff --git a/tests/checksum_test.cpp b/tests/checksum_test.cpp
index 361d33c..781f990 100644
--- a/tests/checksum_test.cpp
+++ b/tests/checksum_test.cpp
@@ -41,10 +41,10 @@
   scudo::u8 IdenticalChecksums = 0;
   for (scudo::uptr I = 0; I < ArraySize; I++) {
     for (scudo::uptr J = 0; J < SCUDO_WORDSIZE; J++) {
-      Array[I] ^= 1U << J;
+      Array[I] ^= scudo::uptr{1} << J;
       if (F(Seed, Array, ArraySize) == Reference)
         IdenticalChecksums++;
-      Array[I] ^= 1U << J;
+      Array[I] ^= scudo::uptr{1} << J;
     }
   }
   // Allow for a couple of identical checksums over the whole set of flips.