Dune 2.6.1

Fix crash when caching is enabled (@rgrinberg, #3581, fixes #3580)

Do not use -output-complete-exe until 4.10.1 as it is broken in 4.10.0 (@jeremiedimino, #3187)

Fix crash when an unknown pform is found (such as %{unknown}) (#3560, @emillon)

Improve error message when invalid package names (such as the empty string) are passed to dune build -p. (#3561, @emillon)

Fix a stack overflow when displaying large outputs (including diffs) (#3537, fixes #2767, #3490, @emillon)

Pass -g when compiling ppx preprocessors (#3671, @rgrinberg)