test_views_info.py: Skip test if required packages are missing

Alternative would be to add .[web] dependencies to .[dev] dependencies.
Noticed because of failing GitHub Action run.

==================================== ERRORS ====================================
__________________ ERROR collecting tests/test_views_info.py ___________________
ImportError while importing test module '/home/runner/work/PatchScope/PatchScope/tests/test_views_info.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
[...]/python3.10/importlib/__init__.py:126: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
tests/test_views_info.py:3: in <module>
    from diffinsights_web.views.info import time_range_options
src/diffinsights_web/views/__init__.py:3: in <module>
    import panel as pn
E   ModuleNotFoundError: No module named 'panel'
=========================== short test summary info ============================

tests/test_views_info.py

@@ -1,5 +1,11 @@
 import datetime
 
+# https://docs.pytest.org/en/stable/how-to/skipping.html#skipping-on-a-missing-import-dependency
+import pytest
+pandas = pytest.importorskip("pandas")
+param = pytest.importorskip("param")
+panel = pytest.importorskip("panel")
+
 from diffinsights_web.views.info import time_range_options