gnucash future: Run coverage tests on ubuntu-26.04.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/122cb6dc (commit)
	from  https://github.com/Gnucash/gnucash/commit/24481321 (commit)



commit 122cb6dcca4d27077767373f527c37dd215e17a7
Author: John Ralls <jralls at ceridwen.us>
Date:   Wed Jun 17 13:29:36 2026 -0700

    Run coverage tests on ubuntu-26.04.
    
    ubuntu-latest isn't latest enough. Recent lcov v2 errors
    out if there are no GCDA files in the target directory.
    Call it with a shell script that checks first.



Summary of changes:
 .github/workflows/coverage.yml         |  4 ++--
 common/cmake_modules/GncCoverage.cmake | 41 ++++++++++++++++++++++++----------
 2 files changed, 31 insertions(+), 14 deletions(-)