v3.5.15 minor update

What's Changed

• Update CHANGES docs for 3.5.12 by @willend in #1770
• Updates to install-docs for McStas/McXtrace 3.5.12 update by @willend in #1771
• No repo solution for 3.5.12 by @willend in #1772
• Update changelogs with repo situation by @willend in #1773
• Adjust test target value by @willend in #1774
• Reorder config dialogue for "small screens" by @willend in #1775
• Let mcstas-antlr produce output for 1-2 SNS instruments by @willend in #1776
• PowderN: fix warning message repeated for ever by @farhi in #1777
• Use DECLARE/INIT vars to set up Mono/Ana by @willend in #1778
• Update SECURITY.md by @willend in #1779
• Patch "basictest" workflows for use of macOS 14/15 by @willend in #1780
• Patch workflows to re-include macOS 13 by @willend in #1781
• Raise a warning dialogue if pyside6 is found. by @willend in #1782
• PR for cmake deb fix (#1783) by @willend in #1787
• Print warning when overwriting COPY EXTEND %{%} block from instance by @willend in #1786
• Two minor fixes by @willend in #1788
• Ensure the MCCODE_MAJOR/MINOR/PATCH vars always have a meaning by @willend in #1789
• ANTLR-support: Replace nasty type var[] in fact headers by @willend in #1790
• Avoid recompile-attempts for failed instruments by @willend in #1792
• McXtrace fixes nightlies by @willend in #1793
• Various minor comp instr fixes by @willend in #1795
• Fix issue 1794 monitor_nd atomic listmode by @willend in #1796

Full Changelog: v3.5.12...v3.5.15