Always cancel in-progress workflows on new commits

The current ``github.head_ref || github.run_id`` syntax only cancels
in-progress GitHub Actions runs triggered by pull requests, as
``head_ref`` is only defined for pull requests, and ``run_id`` is
always unique. This changes to using ``ref``, which is the name of
the branch or tag linked to the commit, meaning that in-progress jobs
will be cancelled on pushes to a branch.

.github/workflows/builddoc.yml

@@ -6,7 +6,7 @@ permissions:
   contents: read
 
 concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
 jobs:

.github/workflows/latex.yml

@@ -6,7 +6,7 @@ permissions:
   contents: read
 
 concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
 jobs:

.github/workflows/lint.yml

@@ -6,7 +6,7 @@ permissions:
   contents: read
 
 concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
 env:

.github/workflows/main.yml

@@ -6,7 +6,7 @@ permissions:
   contents: read
 
 concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
 env:

.github/workflows/nodejs.yml

@@ -6,7 +6,7 @@ permissions:
   contents: read
 
 concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
 jobs: