Add missing ENABLE_TAG_FOR_SINGLE_TAG_CHECKED_PTR

It should've been part of https://crrev.com/c/2306131

Bug: 1092288
Change-Id: I873c8cc804ad15e6970fb00ed0b083c490c10d8a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2307390
Commit-Queue: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Auto-Submit: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789938}

base/allocator/partition_allocator/checked_ptr_support.h

@@ -7,5 +7,6 @@
 
 #define ENABLE_TAG_FOR_CHECKED_PTR2 0
 #define ENABLE_TAG_FOR_MTE_CHECKED_PTR 0
+#define ENABLE_TAG_FOR_SINGLE_TAG_CHECKED_PTR 0
 
 #endif  // BASE_ALLOCATOR_PARTITION_ALLOCATOR_CHECKED_PTR_SUPPORT_H_