CI: auto-fix via zizmor

May include:

- Avoids risky string interpolation.
- Prevents checkout premissions from leaking

Author: tacaswell

.github/workflows/main.yaml

@@ -7,12 +7,16 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
+        with:
+          persist-credentials: false
       - uses: actions/setup-python@v2
       - uses: pre-commit/action@0764670bf370aab253130d534e1eda7ff497dc60 # v2.0.0
   build:
     runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
+        with:
+          persist-credentials: false
       - uses: actions/setup-python@v2
         with:
           python-version: "3.10"