x/build/cmd/watchflakes: fails to parse the "!~" operator

[dmitshur]

Both of these scripts should parse successfully:

default <- pkg == "cmd/go" && output ~ `some regexp`
default <- pkg == "cmd/go" && output !~ `some regexp`

Yet the latter doesn't, producing an "unexpected !" error. See #66337 (comment) and #66337 (comment) for more context.

[gopherbot]

Change https://go.dev/cl/640295 mentions this issue: cmd/watchflakes: add some script parsing tests

[gopherbot]

Change https://go.dev/cl/640275 mentions this issue: cmd/watchflakes/internal/script: lex !~ as a single token