memory-hotplug test from ubuntu_kernel_selftests failed on X-4.4 / X-4.15 / B-4.15 / F-5.4 ARM64 (execution permission issue)

Looks like the cause is the test script become non-executable:
$ ll mem-on-off-test.sh
-rw-r--r-- 1 root root 6120 Jan 28 2018 mem-on-off-test.sh

There is no config change between 4.15.0-114-generic #115~16.04.1 and 4.15.0-112.113~16.04.1

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1892816

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

As this issue does not exist in 4.15.0-112, I will call this a potential regression.

Issue spotted on F-5.4 ARM64 (there is no such issue on amd64 / PowerPC /s390x)

On 5.4 the error message is a bit different:
 # selftests: memory-hotplug: mem-on-off-test.sh
 # Warning: file mem-on-off-test.sh is not executable, correct this.
 not ok 1 selftests: memory-hotplug: mem-on-off-test.sh

For AWS ARM64, this issue can be found on B and F as well.

Test script was executable on the git tree, but not when running the test.

The test uses apt-get source command to get the tree, we used to have this issue on X https://bugs.launchpad.net/bugs/1861973 but this one here seems different as it's not affecting all the other arches.

Failed on Bionic/oracle : 5.4.0-1026.26~18.04.1 : amd64

60. 09/28 06:41:28 DEBUG| utils:0153| [stdout] # ./mem-on-off-test.sh: line 78: echo: write error: Device or resource busy
61. 09/28 06:41:28 DEBUG| utils:0153| [stdout] # offline_memory_expect_success 377: unexpected fail
62. 09/28 06:41:49 DEBUG| utils:0153| [stdout] #
63. 09/28 06:41:49 DEBUG| utils:0153| [stdout] not ok 1 selftests: memory-hotplug: mem-on-off-test.sh # TIMEOUT
64. 09/28 06:41:49 DEBUG| utils:0153| [stdout] make[1]: Leaving directory '/home/ubuntu/autotest/client/tmp/ubuntu_kernel_selftests/src/linux/tools/testing/selftests/memory-hotplug'
65. 09/28 06:41:49 DEBUG| utils:0153| [stdout] make: Leaving directory '/home/ubuntu/autotest/client/tmp/ubuntu_kernel_selftests/src/linux/tools/testing/selftests'
66. 09/28 06:41:49 INFO |ubuntu_ker:0248| ========== Summary ===========
67. 09/28 06:41:49 INFO |ubuntu_ker:0076| Sub test case: mem-on-off-test.sh failed.

Found on Bionic 4.15.0-141.145 arm64 this cycle (sru-20210315)

This is disabled intentionally:
https://kernel.ubuntu.com/git/ubuntu/autotest-client-tests.git/commit/?id=e24a4b63b

I think we can SKIP this test so it won't complain about this anymore.