Make release_note_generator.sh executable

[karandeep-johar]

Checklist

General Contributing

• Have you read the Code of Conduct and signed the CLA?

Is This a Code Change?

• Non-code related change (markdown/git settings etc)
• Code Change
• Example/Test Code Change

Validation

• Have you ran tox?
• Do the tests pass?

[codecov]

Codecov Report

Merging #198 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #198   +/-   ##
=======================================
  Coverage   51.73%   51.73%           
=======================================
  Files          37       37           
  Lines        8367     8367           
  Branches     1786     1786           
=======================================
  Hits         4329     4329           
  Misses       3724     3724           
  Partials      314      314           

Flag	Coverage Δ
#unit	51.73% <ø> (ø)

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