Update test-figure for AR6 Ip / IMP color codes for plotting

[danielhuppmann]

Description of PR

This PR updates the test image for the IPCC color codes for #794.

[codecov]

Codecov Report

Merging #795 (a28ae5e) into fix_imp_colors (48cf774) will decrease coverage by 0.4%.
Report is 27 commits behind head on fix_imp_colors.
The diff coverage is 92.4%.

@@               Coverage Diff                @@
##           fix_imp_colors    #795     +/-   ##
================================================
- Coverage            95.1%   94.7%   -0.4%     
================================================
  Files                  59      62      +3     
  Lines                6017    5996     -21     
================================================
- Hits                 5724    5681     -43     
- Misses                293     315     +22     

Files	Coverage Δ
pyam/_debiasing.py	100.0% <100.0%> (ø)
pyam/aggregation.py	99.2% <100.0%> (+<0.1%)	⬆️
pyam/logging.py	100.0% <100.0%> (+35.1%)	⬆️
pyam/plotting.py	92.9% <100.0%> (+<0.1%)	⬆️
pyam/run_control.py	72.0% <100.0%> (ø)
pyam/statistics.py	85.6% <100.0%> (+<0.1%)	⬆️
pyam/str.py	100.0% <100.0%> (ø)
pyam/testing.py	77.7% <100.0%> (+2.7%)	⬆️
pyam/timeseries.py	96.9% <100.0%> (+<0.1%)	⬆️
pyam/validation.py	100.0% <100.0%> (ø)
... and 27 more

[danielhuppmann]

Please ignore the failing codecov-test, this must be a hiccup in the coverage-comparison.