Fix incorrect type checking in KeyboardBuilder

[WhiteMemory99]

Description

Now the KeyboardBuilder as_markup method checks if the button type is ReplyKeyboardMarkup, which is incorrect because the button type can be either InlineKeyboardButton or KeyboardButton.

Type of change

• Documentation (typos, code examples or any documentation update)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• Test B

Test Configuration:

• Operating System:
• Python version:

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
• My changes generate no new warnings
• 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

[JrooTJunior]

The changes description file is required.

1. towncrier create 674.bugfix (optional step)
2. Write short description to CHANGES/674.bugfix file

[codecov]

Codecov Report

Merging #674 (d3e24b6) into dev-3.x (18a93aa) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           dev-3.x      #674   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files          269       269           
  Lines         5658      5658           
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  Hits          5658      5658           

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

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