Switch Build job Harden Runner to block mode with observed egress

Author: btschwertfeger

.github/workflows/_build.yaml

@@ -30,7 +30,11 @@ jobs:
         uses: step-security/harden-runner@9af89fc71515a100421586dfdb3dc9c984fbf411 # v2.19.4
         with:
           disable-sudo: true
-          egress-policy: audit
+          egress-policy: block
+          allowed-endpoints: >
+            files.pythonhosted.org:443
+            github.com:443
+            pypi.org:443
 
       - name: Checkout repository
         uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0