CI: only for PR & main

This allows to remove the job duplicates detection script that
has its own odities and was badly working with automatic merges.

If ones want to have the CI running on its develoment branch, that
person should create a draft PR.

.github/workflows/ci.yml

@@ -1,29 +1,19 @@
 name: EasyCrypt compilation & check
 
-on: [push,pull_request,merge_group]
+on:
+  push:
+    branches:
+      - 'main'
+  pull_request:
 
 env:
   HOME: /home/charlie
   OPAMYES: true
   OPAMJOBS: 2
 
 jobs:
-  pre_job:
-    name: Check for Duplicates Jobs
-    runs-on: ubuntu-20.04
-    outputs:
-      should_skip: ${{ steps.skip_check.outputs.should_skip }}
-    steps:
-    - uses: fkirc/skip-duplicate-actions@v5
-      id: skip_check
-      with:
-        concurrent_skipping: 'same_content_newer'
-        skip_after_successful_duplicate: 'false'
-
   compile-opam:
     name: EasyCrypt compilation (opam)
-    needs: pre_job
-    if: needs.pre_job.outputs.should_skip != 'true'
     runs-on: ubuntu-20.04
     container:
       image: ghcr.io/easycrypt/ec-build-box
@@ -38,8 +28,6 @@ jobs:
 
   compile-nix:
     name: EasyCrypt compilation (nix)
-    needs: pre_job
-    if: needs.pre_job.outputs.should_skip != 'true'
     env:
       HOME: /home/runner
     runs-on: ubuntu-20.04
@@ -60,8 +48,7 @@ jobs:
 
   check:
     name: Check EasyCrypt Libraries
-    needs: [pre_job, compile-opam]
-    if: needs.pre_job.outputs.should_skip != 'true'
+    needs: compile-opam
     runs-on: ubuntu-20.04
     container:
       image: ghcr.io/easycrypt/ec-build-box
@@ -95,7 +82,6 @@ jobs:
 
   fetch-external-matrix:
     name: Fetch EasyCrypt External Projects Matrix
-    needs: [pre_job]
     runs-on: ubuntu-20.04
     outputs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
@@ -110,8 +96,7 @@ jobs:
 
   external:
     name: Check EasyCrypt External Projects
-    needs: [pre_job, compile-opam, fetch-external-matrix]
-    if: needs.pre_job.outputs.should_skip != 'true'
+    needs: [compile-opam, fetch-external-matrix]
     runs-on: ubuntu-20.04
     container:
       image: ghcr.io/easycrypt/ec-build-box