HTTP checker fails to verify error returned by http.NewRequestWithContext

[alnvdl-work]

The error returned by this line is not being checked:

pebble/internals/overlord/checkstate/checkers.go

Line 54 in 6544671

request, err := http.NewRequestWithContext(ctx, "GET", c.url, nil)

While the most likely error scenario would be invalid URLs (which wouldn't be a problem if the caller is validating the URL beforehand), http.NewRequestWithContext unfortunately makes no guarantees as to when it will returns errors: https://pkg.go.dev/net/http#NewRequestWithContext

[benhoyt]

Thanks! I'm fixing this and other issues over at #580 -- feel free to comment.