Add unit tests for _beacons and wire into CI

Add 100%-coverage unit tests for the three custom salt beacons
(postgres_pillar_beacon, rules_beacon, zeek) and add salt/_beacons to
the python-test workflow's paths trigger and matrix.

To pass the workflow's flake8 lint over the whole directory:
- zeek.py: reindent to 4 spaces, drop trailing blank line, noqa the
  Salt-injected __salt__ references (F821); no logic change.
- postgres_pillar_beacon.py: noqa C901 on beacon() (complexity 13 > 12).

.github/workflows/pythontest.yml

@@ -5,6 +5,7 @@ on:
     paths:
       - "salt/sensoroni/files/analyzers/**"
       - "salt/manager/tools/sbin/**"
+      - "salt/_beacons/**"
 
 jobs:
   build:
@@ -14,7 +15,7 @@ jobs:
       fail-fast: false
       matrix:
         python-version: ["3.14"]
-        python-code-path: ["salt/sensoroni/files/analyzers", "salt/manager/tools/sbin"]
+        python-code-path: ["salt/sensoroni/files/analyzers", "salt/manager/tools/sbin", "salt/_beacons"]
 
     steps:
     - uses: actions/checkout@v3