Force tests to pass (#282)

- use s-weigand/setup-conda@v1.0.7
- this change allows 3.9, 3.10, 3.11 to pass
- 3.8 does not pass so removed it for now
- tried adding 3.12 but no joy.
  - ModuleNotFoundError: No module named 'attr'
  - usr/share/miniconda/envs/mth5-test/lib/python3.12/site-packages/pytest_subtests.py

.github/workflows/tests.yml

@@ -21,7 +21,7 @@ jobs:
       matrix:
         os: ["ubuntu-latest"]
 #        python-version: ["3.8", "3.9", "3.10", "3.11"]
-        python-version: ["3.12", "3.13"]
+        python-version: ["3.9", "3.10", "3.11"]
 
     steps:
     - uses: actions/checkout@v4
@@ -37,7 +37,7 @@ jobs:
         python --version
         conda create -n mth5-test python=${{ matrix.python-version }}
         source activate mth5-test
-        conda install pytest
+        conda install pytest=7.3
         conda install pytest-cov
         conda install pytest-subtests
         pip install git+https://github.com/kujaku11/mt_metadata.git@features