Fix scoped buffer test to init and shut down Platform::Memory.

[bzbarsky-apple]

Problem

TestScopedBuffer is failing due to a merge issue between #2918 and #2987

Summary of Changes

Fix the test to init and shutdown Platform::Memory.

[bzbarsky-apple]

Duplicate of #3050

[github-actions]

Size increase report for "nrfconnect-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

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

sections,vmsize,filesize

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

sections,vmsize,filesize

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

sections,vmsize,filesize