cmd/golangorg: make release.txt less brittle
cmd/golangorg: make release.txt less brittle

CL 421426 extended release.txt coverage to include history entries for
the latest releases, including the currently supported Go 1.19 and 1.18.
Make the test less strict so it doesn't start to fail when future minor
releases come out.

Change-Id: I2864e10f23cf706b1bd4d97e9ae29ac6ea8ad3f3
Reviewed-on: https://go-review.googlesource.com/c/website/+/422637
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Tatiana Bradley <ed5904c3174de8861076818d9fdd7f7c949a16e6@golang.org>
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@google.com>
Auto-Submit: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website