2a95c7c95690112a03b14ccb0fb8f66db12cb75b ci: Check for submodules (Emil Engler)
Pull request description:
See #18019.
The current solution looks like this (I also tested with multiple submodules):
```
These submodules were found, delete them:
355a5a310019659d9bf6818d2fd66fbb214dfed7 curl (curl-7_68_0-108-g355a5a310)
```
The submodule example command was `git submodule add https://github.com/curl/curl.git curl`
ACKs for top commit:
laanwj:
ACK 2a95c7c95690112a03b14ccb0fb8f66db12cb75b
Tree-SHA512: 64bf388123f0a88d12e3e41ff29bc190339377a0615c35dc3f2700bb7773470a8fa426e0ff57188a60ed88bded39f75082ff0b73118651ff403b163422395005
