GHA: optimize test prereq steps

- Linux: move test and pytest prereqs right before test run.
  - returns build phase results faster.
  - allows skipping steps for jobs that don't need them.
  - makes dependencies more transparent.
- sync prereq install step names.
- use `tests/requirements.txt` more.

Closes #15275

.github/workflows/linux32.yml

@@ -61,7 +61,6 @@ jobs:
           sudo dpkg --add-architecture i386
           sudo apt-get update -y
           sudo apt-get install -y --no-install-suggests --no-install-recommends libtool autoconf automake pkgconf stunnel4 ${{ matrix.build.install_packages }}
-          sudo python3 -m pip install --break-system-packages impacket
         name: 'install prereqs'
 
       - uses: actions/checkout@eef61447b9ff4aafe5dcd4e0bbf5d482be7e7871 # v4
@@ -88,6 +87,10 @@ jobs:
       - run: make V=1 -C tests
         name: 'make tests'
 
+      - name: 'install test prereqs'
+        run: |
+          sudo python3 -m pip install --break-system-packages -r tests/requirements.txt
+
       - run: make V=1 test-ci
         name: 'run tests'
         env: