Fix test_bertscore_sorting bug + validate idf arg

[GPPassos]

What does this PR do?

Fixes a test related to bert_score sorting, added on: #2347
Additionally, validates the idf input flag to bert_score.

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements) (Not discussed, but quick fix)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs? (no need IMO)
• Did you write any new necessary tests?

The test was misconfigured, in a way that `idf` was always passed as tuples, which were coerced into `True`. This PR fixes the test and adds a validation step at `bert_score` that checks if the value of `idf` is an actual boolean.

---

📚 Documentation preview 📚: https://torchmetrics--2727.org.readthedocs.build/en/2727/

[GPPassos]

Sorry for the changes in the PR, some commits were meant for a separate branch (at this point, actually related to issue #2728 ). This one should be very basic.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 39%. Comparing base (6bfb775) to head (c32e25c).
Report is 1 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (6bfb775) and HEAD (c32e25c). Click for more details.

HEAD has 82 uploads less than BASE

Flag	BASE (6bfb775)	HEAD (c32e25c)
Windows	6	3
python3.8	6	3
cpu	39	20
torch1.13.1+cpu	6	3
macOS	7	4
python3.10	9	5
torch2.0.1	3	2
torch2.4.0+cpu	2	1
python3.11	6	3
torch1.11.0+cpu	2	1
Linux	26	13
python3.9	18	9
torch2.0.1+cpu	6	3
torch1.12.1+cpu	2	1
gpu	3	0
unittest	3	0
torch1.10.2+cpu	2	1
torch1.13.1	2	1
torch2.3.1+cpu	4	2
torch2.2.2+cpu	4	2
torch2.1.2+cpu	2	1
torch2.4.0+cu121	2	1
torch2.4.0	2	1

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #2727     +/-   ##
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- Coverage      69%     39%    -30%     
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  Files         329     316     -13     
  Lines       18083   17921    -162     
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- Hits        12505    7034   -5471     
- Misses       5578   10887   +5309