CLN: Fix misspelling of indices

DOC: Add description of 2.15.4

Add entries for 2.15.3 and 2.15.2 to history.md

BUG: Fix incorrect undef in roff parameters

import_roff would incorrectly use the undefined values
from xtgeo.GridProperty.undef. Now, import_roff and
export_roff converts to the roff file formats undefined
values.

REL: Release notes for 2.15.1

DOC: Add release notes for version 2.15

TST: increase deadline

FIX: os independent tmpdir and paths

Change from hardcoded "/tmp" to tempfile functions
and also make paths based on pathlib functions

BUG: fixes bug in zmap parser

There was a check that was a bit to strickt, making valid files
be reported as invalid.

Update deploy-xtgeo-pypi.yml