Fix typo in GCP BigQuery client error messages

[Hashim1999164]

Proposed commit message

Fix misspelled GCP BigQuery client error strings in Metricbeat billing and carbon modules (gerror -> error, capitalize BigQuery).

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works.
• I have added an entry in ./changelog/fragments using the changelog tool.

Disruptive User Impact

None. Only user-visible change is corrected wording in two error messages.

How to test this PR locally

Confirm the updated strings in:

• x-pack/metricbeat/module/gcp/billing/billing.go
• x-pack/metricbeat/module/gcp/carbon/carbon.go

Optional: force BigQuery client creation to fail and check the error text.

Related issues

Fixes #51894

[botelastic]

This pull request doesn't have a Team:<team> label.

[cla-checker-service]

💚 CLA has been signed

[github-actions]

🤖 GitHub comments

Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)
• /test : Run the Buildkite pipeline.

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @Hashim1999164? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[Hashim1999164]

I have signed the Elastic Contributor Agreement.