chore(ci): Fix git annex installation

Author: effigies

.github/workflows/python_tests.yml

@@ -47,15 +47,15 @@ jobs:
           python-version: ${{ matrix.python-version }}
 
       - name: Install git-annex ubuntu
-        if: matrix.platform == 'ubuntu-latest'
+        if: matrix.os == 'ubuntu-latest'
         run: conda install -c conda-forge git-annex
 
       - name: Install git-annex macos
-        if: matrix.platform == 'macos-latest'
+        if: matrix.os == 'macos-latest'
         run: brew install git-annex
 
       - name: Install git-annex windows
-        if: matrix.platform == 'windows-latest'
+        if: matrix.os == 'windows-latest'
         uses: crazy-max/ghaction-chocolatey@v3
         with:
           args: install git-annex --yes --ignore-checksums