CI: avoid running slow tests in wheel builds and Emscripten

These are extra tests that iterate over all wavelets and require a lot
of time even on a regular x86-64 build (~10s for `test_precision`, 42s
for `test_swt_iswt` on my machine). For Emscripten and especially under
Qemu (Linux aarch64 wheel builds) they're really really slow.
These tests aren't essential to run for wheel builds, so disable them.

.github/workflows/emscripten.yml

@@ -70,7 +70,7 @@ jobs:
           pushd demo
           pip install matplotlib pytest
           python -c "import pywt; print(pywt.__version__)"
-          pytest --pyargs pywt
+          pytest --pyargs pywt -m "not slow"
 
         # https://anaconda.org/scientific-python-nightly-wheels/pywavelets
         # WARNING: this job will overwrite existing wheels.

.github/workflows/wheel_tests_and_release.yml

@@ -8,7 +8,7 @@ env:
   CIBW_BUILD_VERBOSITY: 2
   # CIBW_BEFORE_BUILD: pip install cython
   CIBW_TEST_REQUIRES: pytest
-  CIBW_TEST_COMMAND: pytest --pyargs pywt
+  CIBW_TEST_COMMAND: pytest --pyargs pywt -m "not slow"
   CIBW_ENVIRONMENT: PIP_PREFER_BINARY=1
 
 jobs: