fix determin lib name varation logic (dotnet#79370)

When checking whether the suffix is contained, the size calcuation is wrong.

In case of Linux, u".so" is defined to PLATFORM_SHARED_LIB_SUFFIX_W.
So, string length (3) should be added to iterator.
But, in the current implementation, ARRAY_SIZE(PLATFORM_SHARED_LIB_SUFFIX_W) (4) is added to iterator.

src/coreclr/vm/nativelibrary.cpp

@@ -549,7 +549,7 @@ namespace
             SString::CIterator it = libName.Begin();
             if (libName.Find(it, PLATFORM_SHARED_LIB_SUFFIX_W))
             {
-                it += ARRAY_SIZE(PLATFORM_SHARED_LIB_SUFFIX_W);
+                it += (ARRAY_SIZE(PLATFORM_SHARED_LIB_SUFFIX_W) - 1);
                 containsSuffix = it == libName.End() || *it == (WCHAR)'.';
             }