Disable DNS tests on Raspberry Pi

[mspang]

These tests don't work on the Pi currently, needs investigation.

See #3312

[github-actions]

Size increase report for "nrfconnect-example-build"

File	Section	File	VM
chip-lighting.elf	[LOAD #1 [RWX]]	12	12
chip-lighting.elf	text	4	4
chip-lock.elf	[LOAD #1 [RWX]]	12	12
chip-lock.elf	text	4	4

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-lighting.elf and ./pull_artifact/chip-lighting.elf:

sections,vmsize,filesize
[LOAD #1 [RWX]],12,12
[Unmapped],0,9
.debug_line,0,5
text,4,4
.debug_loc,0,2

Comparing ./master_artifact/chip-lock.elf and ./pull_artifact/chip-lock.elf:

sections,vmsize,filesize
[LOAD #1 [RWX]],12,12
.debug_line,0,5
text,4,4
.debug_loc,0,2
[Unmapped],0,1

Comparing ./master_artifact/chip-shell.elf and ./pull_artifact/chip-shell.elf:

sections,vmsize,filesize