fix(git): correctly pluralise line_length input validation

[BerkeBat]

Closes:

• Git line_length input validation does not handle plurality #301069

To test/reproduce the fix:

1. Open a project that has an initialized git repository (so that the git commit message text box is available)
2. Type 51 characters (default value, otherwise type 1 more than your git.inputValidationSubjectLength, or your git.inputValidationLength, if the former is un-set).
   a. Observe that the line_length warning says '1 character'
3. Add one more character
   a. Observe that the line_length warning says '2 characters'

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@lszomoru

Matched files:

• extensions/git/src/diagnostics.ts

[BerkeBat]

bumping, quick and easy one 😎