[microsoft/dev.boringcrypto.go1.18] Update VERSION to go1.18

[dagood]

Upstream doesn't maintain this file, so we have our copy that we update. This is ingested into the build asset JSON and used to generate the Dockerfiles, etc. in microsoft/go-images.

This is something I'm eager to get into automatic release infrastructure.

[dagood]

windows-amd64-test failed with flakiness, I hit retry:

##### moved GOROOT
ok  	fmt	0.097s
go tool dist: failed to restore GOROOT: rename D:\a\1\s\go-moved D:\a\1\s\go: Access is denied.

=== Errors
go tool dist: failed to restore GOROOT: rename D:\a\1\s\go-moved D:\a\1\s\go: Access is denied.

DONE 14480 tests, 1127 skipped, 1 error in 1057.878s

This is an example of what we can only assume is a failure caused by antivirus locking. We have this thread about the way it showed up when it was happening in the build stage (now the build stage auto-retries, and we're hitting it in the test stage):

• windows-amd64 build flakiness: "compile.exe: Access is denied." #241

Just pointing it out because it came up recently in a standup meeting about this PR I have open to add auto-retries to this part of the Windows jobs, too:

• Add test retries on Windows CI #475