Fix #1027: Avoid update-changelog to generate an extra line when there are no changes

[araujoarthur0]

Related issue

Closes #1027

Context / Background

update-changelog.py was adding an extra empty line to the section below every time the bot was called while there were no changes in the current release.

<!--- Begin changes - Do not remove -->

<!--- End changes - Do not remove -->

For example: 322a4d3

This extra line gets a linter complaint every time and then causes problems for the next PR.

This is not a common problem because we don't often have no changes, though.
Just now we got the first change.

What change is being introduced by this PR?

• Updating the actions we use to the latest to avoid some warnings.
• No longer adding an extra line in the script when there's no change.

How will this be tested?

Ran it locally against an empty changelog.md and against a filled changelog.md.

[codecov]

Codecov Report

Merging #1029 (8149940) into main (ae757ab) will decrease coverage by 0.10%.
Report is 3 commits behind head on main.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1029      +/-   ##
==========================================
- Coverage   75.11%   75.02%   -0.10%     
==========================================
  Files          26       26              
  Lines        2202     2202              
  Branches      346      346              
==========================================
- Hits         1654     1652       -2     
- Misses        548      550       +2     

see 1 file with indirect coverage changes