Merge #19786: doc: Remove label from good first issue template

fa30d52 doc: Remove label from good first issue template (MarcoFalke)

Pull request description:

  Good first issues aren't that frequent that manually assigning the label is a problem, but this fixes the spam problem (e.g. https://twitter.com/GoodFirstIssues/status/1295455089491161088 )

ACKs for top commit:
  jnewbery:
    ACK fa30d52

Tree-SHA512: 59e7c707637cc328e2443c2b7e5d2c82ef151739ad5afb6cea1a60501318dc8c4c81c95591eed8172581ac99d43cf826dcdd547e096eff1038137853af67a975

Author: fanquake

.github/ISSUE_TEMPLATE/good_first_issue.md

@@ -2,11 +2,13 @@
 name: Good first issue
 about: '(Regular devs only): Suggest a new good first issue'
 title: ''
-labels: good first issue
+labels: ''
 assignees: ''
 
 ---
 
+<!-- Needs the label "good first issue" assigned manually before or after opening -->
+
 <!-- A good first issue is an uncontroversial issue, that has a relatively unique and obvious solution -->
 
 <!-- Motivate the issue and explain the solution briefly -->