keepalive: drop invalid strategy

The `strategy` entries are only applicable in matrix jobs, which this
workflow does not have.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.github/workflows/keepalive.yml

@@ -8,8 +8,6 @@ on:
 jobs:
   job:
     runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
     permissions:
       contents: write
     steps: