build and test directly instead of using opam

it looks like the cram packages do not work right with opam --with-tests

.github/workflows/test.yml

@@ -29,4 +29,7 @@ jobs:
         with:
           ocaml-version: ${{ matrix.ocaml-version }}
 
-      - run: opam pin add FrontC.dev . --yes --with-test
+      - run: opam pin add FrontC . --no-action
+      - run: opam install FrontC --deps-only
+      - run: opam exec -- dune build
+      - run: opam exec -- dune runtest

ctoxml/dune

@@ -5,10 +5,7 @@
   (libraries FrontC))
 
 (env
- (_ (binaries (./ctoxml_bin.exe as ctoxml))))
-
+ (_ (binaries (./ctoxml as ctoxml))))
 
 (cram
-  (package ctoxml)
-  (applies_to test)
   (deps %{bin:ctoxml}))

dune

@@ -1,4 +1,2 @@
 (cram
- (package FrontC)
- (applies_to test.t)
  (deps printc/printc_bin.exe))

dune-project

@@ -1,4 +1,4 @@
-(lang dune 2.8)
+(lang dune 2.7)
 (using menhir 2.0)
 (cram enable)
 (version 4.0.0)
@@ -18,7 +18,7 @@
  (description "FrontC provides a C parser and an OCaml definition \
                of an abstract syntax treee for the C language. It also \
                includes AST pretty-printers in plain and XML formats.")
- (depends (dune (>= 2.8)) menhir)
+ (depends (dune (>= 2.7)) menhir)
  (tags (FrontC C parser XML)))
 
 (package