GHA: tidy up quotes, checkout order, silence Android/CMake warnings

- move checkout step right before use.
- quotes in yaml and bash.
- unfold single-line run commands.
- set `CMAKE_WARN_DEPRECATED=OFF` for CMake with Android NDK to avoid
  a wall of useless deprecation warnings hiding useful output.
  These warnings happen in 3rd-party scripts, and unfixable in curl.

Closes #16042

.github/workflows/http3-linux.yml

@@ -476,7 +476,7 @@ jobs:
 
       - name: 'run tests'
         env:
-          TFLAGS: "${{ matrix.build.tflags }}"
+          TFLAGS: '${{ matrix.build.tflags }}'
         run: |
           source $HOME/venv/bin/activate
           if [ -n '${{ matrix.build.generate }}' ]; then
@@ -492,9 +492,9 @@ jobs:
 
       - name: 'run pytest'
         env:
-          TFLAGS: "${{ matrix.build.tflags }}"
+          TFLAGS: '${{ matrix.build.tflags }}'
           CURL_CI: github
-          PYTEST_ADDOPTS: "--color=yes"
+          PYTEST_ADDOPTS: '--color=yes'
         run: |
           source $HOME/venv/bin/activate
           if [ -n '${{ matrix.build.generate }}' ]; then