fix: multi thread error on matplotlib default backend

[alexbarros]

The following script consistently fails when the multi-threading option is active, entering an infinity loop triggered by matplotlib backend. The fix consists in temporarily changing the backend while creating the plots (ty @fabclmnt for the help with this one).

import pandas as pd
import numpy as np

from pandas_profiling import ProfileReport


def create_dataframes(size=1000, alt=False):
    size = size if not alt else size * 2
    time_steps = np.arange(size)

   df1 =  pd.DataFrame(
        {
            "sin": map(lambda x: round(np.sin(x * np.pi / 180), 2), time_steps),
            "gaussian": map(lambda x: round(x, 2), np.random.normal(0, 1, size)),
        }
    )

    df2 = pd.DataFrame(
        {
            "sin": map(lambda x: round(np.sin(x * np.pi / 180), 2), time_steps),
            "miss2": np.random.choice([0, 1, 2, 3, np.nan], replace=True, size=size),
         }
    )

    return df1, df2


if __name__ == '__main__':
    df1, df2 = create_dataframes()
    prof1 = ProfileReport(df1, title="p1")
    prof2 = ProfileReport(df2, title="p2")
    prof1.to_file("p1.html")
    prof2.to_file("p2.html")

[codecov-commenter]

Codecov Report

Base: 90.90% // Head: 90.90% // No change to project coverage 👍

Coverage data is based on head (02bdfc9) compared to base (36fad3c).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1149   +/-   ##
========================================
  Coverage    90.90%   90.90%           
========================================
  Files          178      178           
  Lines         5090     5090           
========================================
  Hits          4627     4627           
  Misses         463      463           

Flag	Coverage Δ
py3.8-ubuntu-latest-pandas	90.90% <ø> (ø)

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Impacted Files	Coverage Δ
src/pandas_profiling/visualisation/context.py	100.00% <ø> (ø)

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