tools roll-release: Bump branchLegacyCutoff to M96

The tool was getting slow, due to the number of branches being examined.
M96 is the latest stable release. We aren't applying fixes to this or older branches.

Also avoids an issue where the M95 branch was missing a cherry-pick, which the tool wanted to merge with each run.

Change-Id: I8a8b1466c10633d9539725cd4f9b1b0514e41e93
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/75067
Auto-Submit: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>
Commit-Queue: James Price <jrprice@google.com>

docs/origin-trial-changes.md

@@ -62,6 +62,7 @@ The following features have been deprecated and will be removed in M102:
 
 * Swizzling of `vec3` types in `storage` and `uniform` buffers has been fixed for Metal 1.x. [tint:1249](https://crbug.com/tint/1249)
 * Calling a function that returns an unused value no longer produces an FXC compilation error. [tint:1259](https://crbug.com/tint/1259)
+* `abs()` fixed for unsigned integers on SPIR-V backend
 
 ## Changes for M95
 
@@ -74,4 +75,3 @@ The following features have been deprecated and will be removed in M102:
 
 * Hex floats: now correctly errors when the magnitude is non-zero, and the exponent would cause overflow. [tint:1150](https://crbug.com/tint/1150), [tint:1166](https://crbug.com/tint/1166)
 * Identifiers beginning with an underscore are now correctly rejected.  [tint:1179](https://crbug.com/tint/1179)
-* `abs()` fixed for unsigned integers on SPIR-V backend

tools/src/cmd/roll-release/main.go

@@ -49,7 +49,7 @@ const (
 	dawnURL             = "https://dawn.googlesource.com/dawn"
 	tintSubdirInDawn    = "third_party/tint"
 	branchPrefix        = "chromium/"
-	branchLegacyCutoff  = 4590 // Branch numbers < than this are ignored
+	branchLegacyCutoff  = 4664 // Branch numbers < than this are ignored
 )
 
 type branches = map[string]plumbing.Hash