[ci] Change test to launch ci only if flag: pr run ci is on

Author: epernod

.github/workflows/ci.yml

@@ -14,7 +14,16 @@ jobs:
     name: Run on ${{ matrix.os }} with SOFA ${{ matrix.sofa_branch }}
     if: >
       github.event_name == 'push' ||
-      contains(github.event.pull_request.labels.*.name, 'pr: run ci')
+      (
+        github.event_name == 'pull_request' &&
+        (
+          contains(github.event.pull_request.labels.*.name, 'pr: run ci') &&
+          (
+            github.event.action != 'labeled' ||
+            github.event.label.name == 'pr: run ci'
+          )
+        )
+      )
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false