[dune] make lang version coherent

bin/frama-c-build-scripts.sh

dev/dune-workspace.bench

dev/dune-workspace.cover

doc/developer/dune-workspace.bench

doc/developer/examples/acsl_extension_ext_types/dune-project

doc/developer/examples/acsl_extension_foo/dune-project

doc/developer/examples/callstack/dune-project

doc/developer/examples/syntactic_check/dune-project

doc/developer/tutorial/hello/src/dune-project

doc/developer/tutorial/hello/v1-simple/dune-project

doc/developer/tutorial/hello/v2-register/dune-project

doc/developer/tutorial/hello/v3-log/dune-project

doc/developer/tutorial/hello/v4-options/dune-project

doc/developer/tutorial/hello/v5-multiple/dune-project

doc/developer/tutorial/hello/v6-test-with-bug/dune-project

doc/developer/tutorial/hello/v7-doc/dune-project

doc/developer/tutorial/viewcfg/v1-simple/dune-project

doc/developer/tutorial/viewcfg/v2-options/dune-project

doc/developer/tutorial/viewcfg/v3-eva/dune-project

doc/developer/tutorial/viewcfg/v4-bogue/dune-project