ci: updating singularity version from 3.6.4 to 3.7.1

To fix error:
Testing (ubuntu-latest, 3.11)
Unable to build Singularity binary for 3.6.4. Only support versions >=3.7.1

.github/workflows/ci.yaml

@@ -42,7 +42,7 @@ jobs:
 
       - uses: eWaterCycle/setup-singularity@v7
         with:
-          singularity-version: 3.6.4
+          singularity-version: 3.7.1
 
       - name: Install
         shell: bash -el {0}