golang: Add go version 1.20

We should upgrade to Go 1.20, because Go 1.18 is already no longer supported.
("Each major Go release is supported until there are two newer major releases" [1]).
Go 1.20 is the incremental improvement for earlier go 1.19 release.
We skip Go 1.19, because it's also unsupported as soon as Go 1.21 is
released (this is expected to happen in one month [2]).

Please find all details in the official release note:

    https://go.dev/doc/go1.20

It was released on 2023-02-01 [1]. Due to the go promise of compatibility
most software should still compile without any problems.

We need to differentiate between go before 1.19 and go after 1.19, because
go before 1.19 needs TestSCMCredentials patch, while starting from go
1.19 this patch has been applied upstream [3].

[1] https://go.dev/doc/devel/release
[2] https://tip.golang.org/doc/go1.21
[3] https://github.com/golang/go/commit/f839aaa22b66bc556fac72f7396082212d2ef45d

/reviewed-by @kirr
/reviewed-on !1417

component/golang/buildout.cfg

@@ -31,17 +31,25 @@ environment =
   GOROOT_FINAL=${:location}
   ${:environment-extra}
 
-# TestChown and TestSCMCredentials currently fail in a user-namespace
+# TestChown currently fails in a user-namespace
 # https://github.com/golang/go/issues/42525
 # the patches apply to go >= 1.12
 patch-options = -p1
 patches =
   ${:_profile_base_location_}/skip-chown-tests.patch#d4e3c8ef83788fb2a5d80dd75034786f
+
+
+[golang-common-pre-1.19]
+<= golang-common
+
+# TestSCMCredentials fails in a user-namespace if golang version < 1.19
+# https://github.com/golang/go/issues/42525
+patches +=
   ${:_profile_base_location_}/fix-TestSCMCredentials.patch#1d8dbc97cd579e03fafd8627d48f1c59
 
 
 [golang14]
-<= golang-common
+<= golang-common-pre-1.19
 # https://golang.org/doc/install/source#bootstrapFromSource
 url = https://dl.google.com/go/go1.4-bootstrap-20171003.tar.gz
 md5sum = dbf727a4b0e365bf88d97cbfde590016
@@ -64,7 +72,7 @@ setarch = setarch arm
 
 
 [golang1.12]
-<= golang-common
+<= golang-common-pre-1.19
 url = https://golang.org/dl/go1.12.17.src.tar.gz
 md5sum = 6b607fc795391dc609ffd79ebf41f080
 
@@ -73,7 +81,7 @@ environment-extra =
   GOROOT_BOOTSTRAP=${golang14:location}
 
 [golang1.16]
-<= golang-common
+<= golang-common-pre-1.19
 url = https://golang.org/dl/go1.16.13.src.tar.gz
 md5sum = 1c076f952d9af57590a36fa7d36f695a
 
@@ -82,7 +90,7 @@ environment-extra =
   GOROOT_BOOTSTRAP=${golang14:location}
 
 [golang1.17]
-<= golang-common
+<= golang-common-pre-1.19
 url = https://golang.org/dl/go1.17.13.src.tar.gz
 md5sum = 4476707f05cf6915ec1173038dc357a9
 
@@ -91,7 +99,7 @@ environment-extra =
   GOROOT_BOOTSTRAP=${golang14:location}
 
 [golang1.18]
-<= golang-common
+<= golang-common-pre-1.19
 url = https://golang.org/dl/go1.18.9.src.tar.gz
 md5sum = e2caa7c4de49aa77a14c694bfc9a5cd1
 
@@ -102,6 +110,14 @@ md5sum = e2caa7c4de49aa77a14c694bfc9a5cd1
 environment-extra =
   GOROOT_BOOTSTRAP=${golang14:location}
 
+[golang1.20]
+<= golang-common
+url = https://go.dev/dl/go1.20.6.src.tar.gz
+md5sum = 1dc2d18790cfaede7df1e73a1eff8b7b
+# go1.20 requires go1.17.13 to bootstrap (see https://go.dev/doc/go1.20#bootstrap)
+environment-extra =
+  GOROOT_BOOTSTRAP=${golang1.17:location}
+
 # ---- infrastructure to build Go workspaces / projects ----
 
 # gowork is the top-level section that defines Go workspace.