Normalize use of string in git command.

[kakkeshyor]

"gpgSign" instead of "gpgsign" for both invocations: (a) avoids confusion, (b) matches use of camel case as in Git documentation.

Why:

The invocation git config --global x true spells the string x in two different ways. The case is probably not important but to maintain parity with Git documentation the suffix of x should use camel case: gpgSign. Also, having two versions of the same suffix in the same block of text may confuse readers.

Closes: NA

What's being changed (if available, include any code snippets, screenshots, or gifs):

Text formatting of this "reusable text block," located at data/reusables/gpg/set-auto-sign.md, specifying a git invocation that sets Git's global configuration to enable automatic commit-signing, is being changed.

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

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Table of review links

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The table shows the files in the content directory that were changed in this pull request. This helps you review your changes on a staging server. Changes to the data directory are not included in this table.

Source	Review	Production	What Changed
authentication/managing-commit-signature-verification/telling-git-about-your-signing-key.md	fpt ghec ghes@ 3.18 3.17 3.16 3.15 3.14	fpt ghec ghes@ 3.18 3.17 3.16 3.15 3.14	from reusable

Key: fpt: Free, Pro, Team; ghec: GitHub Enterprise Cloud; ghes: GitHub Enterprise Server

🤖 This comment is automatically generated.

[Sharra-writes]

@kakkeshyor Thanks for opening a PR! This is a small change and I don't think the case matters, but I should point out that all the documentation I can find on the site writes it as gpgsign, so if your goal is consistency and avoiding user confusion, I don't think this will achieve either of those.

[kakkeshyor]

As you wish.