CMake: Bump downloaded SUNDIALS version

[ZedThree]

Importantly, includes fixes that avoid clobbering our CMake variables

[ZedThree]

Failing on the coverage build with:

Capturing coverage data from /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src
geninfo cmd: '/usr/bin/geninfo /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src --output-filename coverage.info --memory 0'
Found gcov version: 13.3.0
Using intermediate gcov format
Writing temporary data to /tmp/geninfo_datv9fR
Scanning /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src for .gcda files ...
Found 117 data files in /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src
Processing /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src/sys/expressionparser.cxx.gcda
geninfo: WARNING: /home/runner/work/BOUT-dev/BOUT-dev/externalpackages/fmt/include/fmt/core.h:425: unexecuted block on non-branch line with non-zero hit count.  Use "geninfo --rc geninfo_unexecuted_blocks=1 to set count to zero.
Processing /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src/sys/type_name.cxx.gcda
Processing /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src/sys/boutcomm.cxx.gcda
Processing /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src/sys/optionsreader.cxx.gcda
geninfo: WARNING: /usr/include/c++/13/bits/allocator.h:163: unexecuted block on non-branch line with non-zero hit count.  Use "geninfo --rc geninfo_unexecuted_blocks=1 to set count to zero.
	(use "geninfo --ignore-errors gcov,gcov ..." to suppress this warning)
Processing /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src/sys/range.cxx.gcda
Processing /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src/sys/options/options_netcdf.cxx.gcda
geninfo: WARNING: /usr/include/c++/13/bits/stl_iterator_base_funcs.h:151: unexecuted block on non-branch line with non-zero hit count.  Use "geninfo --rc geninfo_unexecuted_blocks=1 to set count to zero.
	(use "geninfo --ignore-errors gcov,gcov ..." to suppress this warning)
Processing /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src/sys/options/options_io.cxx.gcda
geninfo: WARNING: /usr/include/c++/13/bits/range_access.h:86: unexecuted block on non-branch line with non-zero hit count.  Use "geninfo --rc geninfo_unexecuted_blocks=1 to set count to zero.
	(use "geninfo --ignore-errors gcov,gcov ..." to suppress this warning)
Processing /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src/sys/options/options_adios.cxx.gcda
stdout:
  Creating 'options_adios.cxx##646e4f50ed[37](https://github.com/boutproject/BOUT-dev/actions/runs/12931707530/job/36066221774#step:12:38)0643a4092f3b77c200f1.gcov.json.gz'
  No executable lines
stderr:
  /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src/sys/options/options_adios.cxx.gcno:no functions found
  /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src/sys/options/options_adios.cxx.gcda:not a gcov data file
geninfo: ERROR: GCOV failed for /home/runner/work/BOUT-dev/BOUT-dev/build/CMakeFiles/bout++.dir/src/sys/options/options_adios.cxx.gcda!
	(use "geninfo --ignore-errors gcov ..." to bypass this error)

If I had to guess, it's because we're not linking against adios2 on this build so options_adios.cxx is essentially empty. Not sure why that's suddenly a problem here!

Options are probably:

• link against adios in this build (see other PR!)
• work out how to pass --ignore-errors to the right thing
• when add relevant files to CMake sources list depending on options
• remove the coverage build entirely! Not sure we actually ever use this information any more

[dschwoerer]

I am happy to remove the coverage run. I have not looked at the results in years ...