When running unit tests, usually QStandardPaths TestMode is enabled so as
not to mess up the config files in the home dir of the dev running the unit
tests; sGlobalFileName, a global static, was defined only once, which meant
that if KSharedConfig::openConfig() is called before the unit test has had
a chance to call QStandardPaths::setTestModeEnabled(true), then sGlobalFileName
will go on referring to the wrong kdeglobals file (as can be seen in
dfaure's debugging of the issue at [1]). Change the code so as to
detect QStandardPaths TestMode status and change sGlobalFileName as needed.

All unit tests still pass.

[1] https://invent.kde.org/frameworks/kio/-/merge_requests/77#note_74124

While the API might have been once designed to allow random byte strings
to be used as ids and only converted QString to UTF-8, the current
implementation in many places assumes the byte strings passed via
const char* or QByteArray are also in of UTF-8 encoding
(or at least ASCII7-only).
See e.g. KConfigGroup::entryMap() or KConfigGroup::name().

Stating the supported encoding explicitly should avoid any misassumptions.

In case of conflict in i18n, keep the version of the branch "ours"
To resolve a particular conflict, "git checkout --ours path/to/file.desktop"

See https://community.kde.org/Frameworks/Frameworks_Logging_Policy