ci: use Ubuntu 20.04 as the default Docker container #22388

1. 
   fanquake commented at 2:58 AM on July 2, 2021: member

   All but 2 of the Ubuntu CIs (native qt5 & nowallet) are already using 20.04 or 21.04.

2. ci: use Ubuntu 20.04 as the default Docker container

   All but 2 of the Ubuntu CIs are already using 20.04 or 21.04.

   7fc1e14ce6
3. fanquake added the label Tests on Jul 2, 2021
4. fanquake requested review from MarcoFalke on Jul 2, 2021
5. 
   MarcoFalke commented at 5:28 AM on July 2, 2021: member

   This is only relevant when running the "default" stage.

   cr ACK 7fc1e14ce60d4e0533c7ccc65a9b24052d7a608f

6. MarcoFalke merged this on Jul 2, 2021
7. MarcoFalke closed this on Jul 2, 2021

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8. fanquake deleted the branch on Jul 2, 2021
9. fanquake locked this on Jul 2, 2021

Review Requested
MarcoFalke