CI: fix old typo

Author: MuellerSeb

.github/workflows/main.yml

@@ -23,7 +23,7 @@ jobs:
       - uses: actions/checkout@v2
 
       - name: Set up Python 3.8
-        uses: actions\setup-python@v2
+        uses: actions/setup-python@v2
         with:
           python-version: 3.8
 
@@ -86,7 +86,7 @@ jobs:
           fetch-depth: '0'
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions\setup-python@v2
+        uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python-version }}