GHA: use pip requirements.txt with pins, and more venv

- requirements.txt: shorten copyright headers.

- requirements.txt: pin packages to versions.

- GHA/windows: use `tests/requirements.txt`.
  Pick a `cryptography` package version that satifies both `impacket`
  and pytests dependencies.

- GHA/checksrc: move pip deps into a new `requirements.txt`.
  To make Dependabot detect and bump them.

- GHA/checksrc: replace apt packages for python test deps with pip
  install `tests/**/requirements.txt` to a venv.

- GHA/checksrc: use venv and drop `--break-system-packages`.

- GHA/linux: fix to actually activate venvs.
  Follow-up to 2638570241 #15578

- GHA/linux: fixup (did not cause an issue)
  Follow-up to d75785c7de #18660

- GHA: create venvs later, simplify commands.

- GHA: sync pip command-line options, e.g. drop progress-bar,
  everywhere.

Assisted-by: Dan Fandrich

Closes #18708

.github/workflows/http3-linux.yml

@@ -512,7 +512,6 @@ jobs:
             libpsl-dev libbrotli-dev libzstd-dev zlib1g-dev libidn2-0-dev libldap-dev libuv1-dev \
             ${INSTALL_PACKAGES} \
             ${MATRIX_INSTALL_PACKAGES}
-          python3 -m venv ~/venv
           echo 'CC=gcc-12' >> "$GITHUB_ENV"
           echo 'CXX=g++-12' >> "$GITHUB_ENV"
 
@@ -726,8 +725,8 @@ jobs:
       - name: 'install test prereqs'
         if: ${{ !contains(matrix.build.install_steps, 'skipall') && !contains(matrix.build.install_steps, 'skiprun') }}
         run: |
-          source ~/venv/bin/activate
-          python3 -m pip install -r tests/requirements.txt
+          python3 -m venv ~/venv
+          ~/venv/bin/pip --disable-pip-version-check --no-input --no-cache-dir install --progress-bar off --prefer-binary -r tests/requirements.txt
 
       - name: 'run tests'
         if: ${{ !contains(matrix.build.install_steps, 'skipall') && !contains(matrix.build.install_steps, 'skiprun') }}
@@ -744,8 +743,8 @@ jobs:
       - name: 'install pytest prereqs'
         if: ${{ !contains(matrix.build.install_steps, 'skipall') && !contains(matrix.build.install_steps, 'skiprun') }}
         run: |
-          source ~/venv/bin/activate
-          python3 -m pip install -r tests/http/requirements.txt
+          [ -d ~/venv ] || python3 -m venv ~/venv
+          ~/venv/bin/pip --disable-pip-version-check --no-input --no-cache-dir install --progress-bar off --prefer-binary -r tests/http/requirements.txt
 
       - name: 'run pytest event based'
         if: ${{ !contains(matrix.build.install_steps, 'skipall') && !contains(matrix.build.install_steps, 'skiprun') }}