Suppress modified changes for files which weren't actually modified in JSON output.

[cr1901]

Right now, if borg diff is run with the --json-lines parameter (and without --content-only, files whose content have not been modified will still be given a modified entry of {"added": 0, "removed": 0, "type": "modified"}, e.g.:

 {"changes": [{"added": 0, "removed": 0, "type": "modified"}, {"new_ctime": "2024-07-22T20:13:59.352959", "old_ctime": "2020-01-06T02:21:13.955255", "type": "ctime"}], "path": ".areca/workspace/.log/areca.12-06-24.log"}

Per IRC discussion, this is considered a bug, as the file's content was not actually changed, and thus shouldn't be in the changes JSON array. This PR fixes the behavior so that JSON entries no longer get a "type": "modified" object for files whose contents weren't changed, but ctime, mtime, etc were changed. E.g.:

{"changes": [{"new_ctime": "2024-07-22T20:13:59.352959", "old_ctime": "2020-01-06T02:21:13.955255", "type": "ctime"}], "path": ".areca/workspace/.log/areca.12-06-24.log"}

Text output (without --json-lines) is unaffected; I feel that the 0 B 0 B is more useful for humans looking at output, compared to JSON processors :):

      0 B       0 B [ctime: Mon, 2020-01-06 02:21:13 -> Mon, 2024-07-22 20:13:59] .areca/workspace/.log/areca.12-06-24.log

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.73%. Comparing base (adf2d8c) to head (938e144).
Report is 7 commits behind head on 1.4-maint.

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Additional details and impacted files

@@              Coverage Diff              @@
##           1.4-maint    #8334      +/-   ##
=============================================
+ Coverage      82.69%   82.73%   +0.03%     
=============================================
  Files             38       38              
  Lines          11045    11049       +4     
  Branches        2122     2123       +1     
=============================================
+ Hits            9134     9141       +7     
+ Misses          1345     1344       -1     
+ Partials         566      564       -2     

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[ThomasWaldmann]

@cr1901 OK, guess this is ready to merge?

[cr1901]

@ThomasWaldmann Okay to merge.

[ThomasWaldmann]

@cr1901 Thanks!

[ThomasWaldmann]

Guess a forward port to master branch would be good.

1.2-maint will be phased out in a while, so a backport to there is optional.