Enable tests/scalar and test/series in cudf.pandas tests (#15486)

Locally these don't seem to hang or crash workers

Authors:
  - Matthew Roeschke (https://github.com/mroeschke)

Approvers:
  - GALI PREM SAGAR (https://github.com/galipremsagar)

URL: #15486

python/cudf/cudf/pandas/scripts/run-pandas-tests.sh

@@ -27,8 +27,6 @@ PYTEST_IGNORES="--ignore=tests/interchange/test_impl.py \
 --ignore=tests/window/test_numba.py \
 --ignore=tests/window \
 --ignore=tests/plotting \
---ignore=tests/scalar \
---ignore=tests/series/test_arithmetic.py \
 --ignore=tests/tslibs/test_parsing.py \
 --ignore=tests/io/parser/common/test_read_errors.py"