meta: use platform dropdown on flaky template

PR-URL: #43855
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

.github/ISSUE_TEMPLATE/4-report-a-flaky-test.yml

@@ -19,11 +19,24 @@ body:
  placeholder: e.g. `test-fs-stat-bigint`
  validations:
  required: true
- - type: input
+ - type: dropdown
  attributes:
  label: Platform
  description: The platform the test is flaky on.
- placeholder: e.g. `macos` or `linux`
+ multiple: true
+ options:
+ - AIX
+ - FreeBSD
+ - Linux ARM64
+ - Linux ARMv7
+ - Linux PPC64LE
+ - Linux s390x
+ - Linux x64
+ - macOS ARM64
+ - macOS x64
+ - SmartOS
+ - Windows
+ - Other
  - type: textarea
  attributes:
  label: Console output