Bump eWaterCycle/setup-singularity from 6 to 7

Bumps [eWaterCycle/setup-singularity](https://github.com/eWaterCycle/setup-singularity) from 6 to 7.
- [Release notes](https://github.com/eWaterCycle/setup-singularity/releases)
- [Commits](eWaterCycle/setup-singularity@v6...v7)

---
updated-dependencies:
- dependency-name: eWaterCycle/setup-singularity
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci-tests.yml

@@ -37,7 +37,7 @@ jobs:
 
       - name: Set up Singularity
         if: ${{ matrix.step == 'unit' || matrix.step == 'mypy' }}
-        uses: eWaterCycle/setup-singularity@v6
+        uses: eWaterCycle/setup-singularity@v7
         with:
           singularity-version: ${{ env.singularity_version }}
 
@@ -123,7 +123,7 @@ jobs:
       - uses: actions/checkout@v2
 
       - name: Set up Singularity
-        uses: eWaterCycle/setup-singularity@v6
+        uses: eWaterCycle/setup-singularity@v7
         with:
           singularity-version: ${{ env.singularity_version }}