autoversion: Mark Go 1.17, 1.18, and 1.19 as using Unicode 13.

Issues upstream:
 - unicode: update to version 14.0
    → golang/go#48621
 - unicode: update to version 15.0
    → golang/go#55079

At the moment, Unicode 15 is on the roadmap for Go 1.20, while Go 1.19
is confirmed to still be using Unicode 13 (e.g. on Debian unstable and
Debian testing).

autoversion/textseg/unicode13.go

@@ -1,4 +1,4 @@
-// +build go1.16,!go1.17
+// +build go1.16,go1.17,go1.18,go1.19,!go1.20
 
 package textseg