internal/releasetargets: set LongTestBuilder for linux-arm64

The linux/arm64 port is first class and a longtest builder was added
for it during the Go 1.20 development cycle. It's a mandatory trybot
on 1.20+ release branches and is working well.

The builder recently found a real problem in go.dev/issue/60825, which
has been resolved by now. Upgrade this builder from an advisory TryBot
to have more complete release test coverage.

For golang/go#40561.
For golang/go#49649.
For golang/go#29252.

Change-Id: I1765e820deb0d34b7bb9a72aba397d87c1369ced
Reviewed-on: https://go-review.googlesource.com/c/build/+/504525
Run-TryBot: Dmitri Shuralyov <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>

internal/releasetargets/releases.txt

@@ -74,6 +74,7 @@ linux-amd64     linux      amd64      linux-amd64-bullseye
 	Running on GCP
 
 linux-arm64     linux      arm64      linux-arm64
+	Long tests on linux-arm64-longtest
 	Running on GCP
 
 linux-armv6l    linux      arm        linux-arm-aws
@@ -134,6 +135,7 @@ linux-amd64     linux      amd64      linux-amd64-bullseye
 	Running on GCP
 
 linux-arm64     linux      arm64      linux-arm64
+	Long tests on linux-arm64-longtest
 	Running on GCP
 
 linux-armv6l    linux      arm        linux-arm-aws

internal/releasetargets/releasetargets.go

@@ -145,6 +145,10 @@ var allReleases = map[int]ReleaseTargets{
 			Builder:         "linux-386-bullseye",
 			LongTestBuilder: "linux-386-longtest",
 		},
+		"linux-arm64": &Target{
+			Builder:         "linux-arm64",
+			LongTestBuilder: "linux-arm64-longtest",
+		},
 		"linux-amd64": &Target{
 			Builder:         "linux-amd64-bullseye",
 			LongTestBuilder: "linux-amd64-longtest",