RFR: 8255412: Add "Linux x32" to platform selection default in custom submit workflow

[Aleksey Shipilev]

I realized that JDK-8254282 missed "Linux x32" for the platform selection. While you can guess it is accepted from reading the workflow, it would be more convenient to have it in the default argument list.

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Commit messages:
 - 8255412: Add "Linux x32" to platform selection default in custom submit workflow

Changes: https://git.openjdk.java.net/jdk/pull/869/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=869&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255412
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/869.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/869/head:pull/869

PR: https://git.openjdk.java.net/jdk/pull/869