Add cs.pp extension to C#

[DecimalTurn]

Adding cs.pp extension to C# per #6662

Checklist:

• I am adding a new extension to a language.
  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension (2.4k+ results):
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A*.cs.pp+using
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • https://github.com/vpenades/CodeSugar/blob/main/src/CodeSugar.System.IO.Sources/_CodeSugarIO.DriveInfo.cs.pp
    • Sample license(s): MIT
  • I have [NOT] included a change to the heuristics to distinguish my language from others using the same extension [since this extension is unique to C#].

[DecimalTurn]

The error during the checks seems unrelated.

It looks like it could be due to https://github.com/tabatkins/bikeshed now redirecting to https://github.com/speced/bikeshed.

[lildude]

It looks like it could be due to https://github.com/tabatkins/bikeshed now redirecting to https://github.com/speced/bikeshed.

Nope. It's because https://github.com/tiabeast/vscode-vba-json has gone AWOL:

[...]
Cloning into '/home/runner/work/linguist/linguist/vendor/grammars/vscode-vba-json'...
fatal: could not read Username for 'https://github.com/': No such device or address
fatal: clone of 'https://github.com/tiabeast/vscode-vba-json.git' into submodule path '/home/runner/work/linguist/linguist/vendor/grammars/vscode-vba-json' failed
Failed to clone 'vendor/grammars/vscode-vba-json'. Retry scheduled
Cloning into '/home/runner/work/linguist/linguist/vendor/grammars/vscode-vba-json'...
fatal: could not read Username for 'https://github.com/': No such device or address
fatal: clone of 'https://github.com/tiabeast/vscode-vba-json.git' into submodule path '/home/runner/work/linguist/linguist/vendor/grammars/vscode-vba-json' failed
[...]

I've just merged #6678 which switches sources.

[lildude]

LGTM. Thanks.

Note: this PR will not be merged until close to when the next release is made. See here for more details.