AIRFLOW-2143a - Fix TaskTries graph counts off-by-1

[mcw0933]

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[mcw0933]

This PR is the same work as in #5297, but based off the v1-10-test branch as requested by @kaxil

[kaxil]

Thanks @mcw0933 - Can we change this for airflow/www_rbac folder too, please? thanks

[mcw0933]

Ok - changes are made to both views.py

[codecov-io]

Codecov Report

Merging #6526 into v1-10-test will increase coverage by <.01%.
The diff coverage is 57.14%.

@@              Coverage Diff               @@
##           v1-10-test    #6526      +/-   ##
==============================================
+ Coverage       79.63%   79.63%   +<.01%     
==============================================
  Files             518      518              
  Lines           35269    35267       -2     
==============================================
  Hits            28086    28086              
+ Misses           7183     7181       -2

Impacted Files	Coverage Δ
airflow/www/views.py	45.03% <0%> (+0.05%)	⬆️
airflow/models/taskinstance.py	93.67% <100%> (+0.02%)	⬆️
airflow/www_rbac/views.py	75.61% <50%> (+0.1%)	⬆️
airflow/jobs/local_task_job.py	85.71% <0%> (-4.77%)	⬇️
airflow/utils/dag_processing.py	59.02% <0%> (+0.32%)	⬆️

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