chore: Updates documentation & GHA workflows to use develop branch

[timnolte]

All Submissions:

• Have you followed the plugin Contributing guideline?
• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

• Updates the GitHub Actions workflows to target the develop branch.
• Updates documentation to reference the develop branch.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?

[github-actions]

Coverage report for commit: cbcd9f1
File: clover.xml

Cover ┌─────────────────────────┐ Freq.
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      └─────────────────────────┘
 *Legend:* █ = Current Distribution 

Summary - Lines: 0.93% | Methods: 1.01%

Files	Lines	Methods	Branches
/workspaces/openid-connect-generic/includes
functions.php	-	100.00%	100.00%
openid-connect-generic-client-wrapper.php	-	-	100.00%
openid-connect-generic-client.php	-	-	100.00%
openid-connect-generic-login-form.php	-	-	100.00%
openid-connect-generic-option-logger.php	-	-	100.00%
openid-connect-generic-option-settings.php	47.37%	12.50%	100.00%
openid-connect-generic-settings-page.php	-	-	100.00%
/workspaces/openid-connect-generic
openid-connect-generic.php	1.77%	-	100.00%

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