.github: fix templates with multiple labels

Also Go2 -> v2

Change-Id: Icde8ffc4a1ee2e43241a3dcd00ff0c48992b1e25
Reviewed-on: https://go-review.googlesource.com/c/go/+/514175
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@golang.org>

.github/ISSUE_TEMPLATE/03-gopls.md

@@ -2,7 +2,9 @@
 name: Gopls bugs or feature requests
 about: Issues or feature requests for the Go language server (gopls)
 title: "x/tools/gopls: "
-labels: gopls Tools
+labels:
+  - gopls
+  - Tools
 ---
 
 <!--

.github/ISSUE_TEMPLATE/11-language-change.md

@@ -2,7 +2,10 @@
 name: Language Change Proposals
 about: Changes to the language
 title: "proposal: Go 2: "
-labels: Proposal Go2 LanguageChange
+labels:
+  - Proposal
+  - v2
+  - LanguageChange
 ---
 
 <!--