Fix send_copy helper parse mode

[mahenzon]

Description

If you set default parse mode on Bot instance, this parse mode applies on all calls with UNSET parse mode, even on send_copy, where entities are already applied and no parse mode is required. It even breaks copying regular messages with 'special' characters like . or ! when MarkdownV2 is set by default.
Parse mode should not be sent, but we need to have an option to override it. So, by default parse_mode in send_copy should be `None.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Added autotests
• Created a Bot instance with default parse_mode = MarkdownV2

Test Configuration:

• Operating System: macOS
• Python version: 3.11

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[github-actions]

✔️ Changelog found.

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[codecov]

Codecov Report

Merging #1332 (05531e4) into dev-3.x (6738255) will not change coverage.
Report is 2 commits behind head on dev-3.x.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff            @@
##           dev-3.x     #1332   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          369       369           
  Lines         9429      9435    +6     
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+ Hits          9429      9435    +6     

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
aiogram/types/message.py	100.00% <ø> (ø)

... and 2 files with indirect coverage changes