INA236: Handle negative current readings correctly (AEGHB-1100)

[brokenpotatoes]

I recently made board with ESP32-S3 and INA236 sensor. My current shunt polarity was inverted thus current readings were nominally negative. The sensor returns the value as a standard two's complement int16. The current implementation detects that the negative sign bit is set and ignores the reading and returns 0. This commit fixes the handling of this value by simply casting the value to int16_t before doing the scaling. The commit was tested on my board.

[CLAassistant]

All committers have signed the CLA.

[github-actions]

	Warnings
⚠️	Some issues found for the commit messages in this PR: the commit message "INA236: Handle negative current readings correctly": type/action should start with a lowercase letter type/action should be one of [change, ci, docs, feat, fix, refactor, remove, revert, test] Please fix these commit messages - here are some basic tips: follow Conventional Commits style correct format of commit message should be: <type/action>(<scope/component>): <summary>, for example fix(esp32): Fixed startup timeout issue allowed types are: change,ci,docs,feat,fix,refactor,remove,revert,test sufficiently descriptive message summary should be between 20 to 72 characters and start with upper case letter avoid Jira references in commit messages (unavailable/irrelevant for our customers) TIP: Install pre-commit hooks and run this check when committing (uses the Conventional Precommit Linter).
⚠️	The source branch "INA236_NEGATIVE_CURRENT" incorrect format: contains uppercase letters. This can cause troubles on case-insensitive file systems (macOS). Please rename your branch.

👋 Hello brokenpotatoes, we appreciate your contribution to this project!

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