fix: Allow multiple builds on staging branch (#20515)

as mentioned on [zulip](https://leanprover.zulipchat.com/#narrow/channel/287929-mathlib4/topic/ci.20on.20master.20is.20failing/near/492095011), staging CI fails, which we don't want.
This pr allows multiple build runs on the `staging` branch at a time, which should hopefully fix the issue

.github/build.in.yml

@@ -15,7 +15,8 @@ env:
 concurrency:
   # label each workflow run; only the latest with each label will run
   # workflows on master get more expressive labels
-  group: ${{ github.workflow }}-${{ github.ref }}.${{(github.ref == 'refs/heads/master' && github.run_id) || ''}}
+  group: ${{ github.workflow }}-${{ github.ref }}.
+    ${{ ( contains(fromJSON( '["refs/heads/master", "refs/heads/staging"]'), github.ref ) && github.run_id) || ''}}
   # cancel any running workflow with the same label
   cancel-in-progress: true
 

.github/workflows/bors.yml

@@ -25,7 +25,8 @@ env:
 concurrency:
   # label each workflow run; only the latest with each label will run
   # workflows on master get more expressive labels
-  group: ${{ github.workflow }}-${{ github.ref }}.${{(github.ref == 'refs/heads/master' && github.run_id) || ''}}
+  group: ${{ github.workflow }}-${{ github.ref }}.
+    ${{ ( contains(fromJSON( '["refs/heads/master", "refs/heads/staging"]'), github.ref ) && github.run_id) || ''}}
   # cancel any running workflow with the same label
   cancel-in-progress: true
 

.github/workflows/build.yml

@@ -32,7 +32,8 @@ env:
 concurrency:
   # label each workflow run; only the latest with each label will run
   # workflows on master get more expressive labels
-  group: ${{ github.workflow }}-${{ github.ref }}.${{(github.ref == 'refs/heads/master' && github.run_id) || ''}}
+  group: ${{ github.workflow }}-${{ github.ref }}.
+    ${{ ( contains(fromJSON( '["refs/heads/master", "refs/heads/staging"]'), github.ref ) && github.run_id) || ''}}
   # cancel any running workflow with the same label
   cancel-in-progress: true
 

.github/workflows/build_fork.yml

@@ -29,7 +29,8 @@ env:
 concurrency:
   # label each workflow run; only the latest with each label will run
   # workflows on master get more expressive labels
-  group: ${{ github.workflow }}-${{ github.ref }}.${{(github.ref == 'refs/heads/master' && github.run_id) || ''}}
+  group: ${{ github.workflow }}-${{ github.ref }}.
+    ${{ ( contains(fromJSON( '["refs/heads/master", "refs/heads/staging"]'), github.ref ) && github.run_id) || ''}}
   # cancel any running workflow with the same label
   cancel-in-progress: true