Rename first job and make the others independent

We actually don't need to dependency because the workspace is not
persisted between jobs anyway.

.github/workflows/ci.yml

@@ -3,7 +3,7 @@ name: Continuous integration
 on: [push, pull_request]
 
 jobs:
-  check_pr:
+  test:
     runs-on: ubuntu-latest
     steps:
       - name: Create npm configuration
@@ -18,7 +18,6 @@ jobs:
 
   install_stable:
     runs-on: ubuntu-latest
-    needs: check_pr
     steps:
       - uses: actions/checkout@v1
       - uses: ./
@@ -27,7 +26,6 @@ jobs:
 
   install_nightly:
     runs-on: ubuntu-latest
-    needs: check_pr
     steps:
       - uses: actions/checkout@v1
       - uses: ./
@@ -39,7 +37,6 @@ jobs:
   install_stable_in_docker:
     runs-on: ubuntu-latest
     container: ubuntu:latest  # Docker image, not the GitHub Actions VM
-    needs: check_pr
     steps:
       # `rustup` will need `curl` or `wget` later
       - run: apt-get update && apt-get install -y curl
@@ -50,7 +47,6 @@ jobs:
 
   install_stable_through_rust_toolchain_file:
     runs-on: ubuntu-latest
-    needs: check_pr
     steps:
       - uses: actions/checkout@v1
       - run: echo "stable" > ./rust-toolchain