CI: improvements in test reliability and performance

- CI default: raise parallelism to 20
- CI valgind: set parallelism to 6
- CI non-native: adapt parallelism for OS builds
- CI Windows: no longer ignore FTP, TFTP, MQTT and SMTP
- CI Windows: restrict test timeout to 10 minutes
- CI Windows: do not run tests for msh3 build
- tests, various: restrict curl invocation to ipv4 to avoid talking to
  any ipv6 test server running in parallel
- tests: requiring http/2 server no longer needs to mention http server
- test 190: use a fixed timeout of 10 seconds instead of %FTPTIME2, as
  that value rises under parallel load beyond what the server is waiting
  and then produces different results
- test 1540: add debug logging
- testrunner: add verify checks for http/2 and http/3 server

Closes #15040

.github/workflows/non-native.yml

@@ -66,7 +66,7 @@ jobs:
             bld/src/curl --disable --version
             if [ '${{ matrix.arch }}' = 'x86_64' ]; then  # Slow on emulated CPU
               cmake --build bld --config Debug --parallel 3 --target testdeps
-              export TFLAGS='-j0'  # flakies: ~389 ~392 ~TFTP and more
+              export TFLAGS='-j4'
               cmake --build bld --config Debug --target test-ci
             fi
             echo '::group::build examples'
@@ -146,7 +146,7 @@ jobs:
             src/curl --disable --version
             if [ '${{ matrix.arch }}' = 'x86_64' ]; then  # Slow on emulated CPU
               make -j3 -C tests
-              make test-ci V=1 TFLAGS='-j8 ~FTP'
+              make test-ci V=1 TFLAGS='-j4'
             fi
             echo '::group::build examples'
             make -j3 examples
@@ -176,7 +176,6 @@ jobs:
             bld/src/curl --disable --version
             if [ '${{ matrix.arch }}' = 'x86_64' ]; then  # Slow on emulated CPU
               cmake --build bld --config Debug --parallel 3 --target testdeps
-              export TFLAGS='-j8 ~FTP'
               cmake --build bld --config Debug --target test-ci
             fi
             echo '::group::build examples'
@@ -206,7 +205,7 @@ jobs:
             gmake -j3 install
             src/curl --disable --version
             gmake -j3 -C tests
-            gmake test-ci V=1 TFLAGS='-j12 ~MQTT ~FTP'
+            gmake test-ci V=1
             echo '::group::build examples'
             gmake -j3 examples
             echo '::endgroup::'