Use built-in GITHUB_ACTIONS variable instead of custom IS_GITHUB_CI

[albertvillanova]

This PR replaces the custom IS_GITHUB_CI environment variable with the GITHUB_ACTIONS variable that GitHub Actions sets automatically.

Motivation

The slow_tests Make target only writes a pytest report log when running in CI, and this was signalled by an IS_GITHUB_CI variable declared in the slow tests workflow. GitHub Actions already exports GITHUB_ACTIONS=true on every runner, so the custom variable is redundant.

Changes

• Use GITHUB_ACTIONS instead of IS_GITHUB_CI to enable the pytest report log in the slow_tests Make target
• Drop the IS_GITHUB_CI environment variable from the slow tests workflow

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Note

Low Risk
Small CI/Makefile change with no application or security impact; report logging still only runs when GitHub Actions sets GITHUB_ACTIONS.

Overview
The slow tests workflow no longer sets a custom IS_GITHUB_CI env var. The slow_tests Make target now gates pytest --report-log slow_tests.log on GitHub’s built-in GITHUB_ACTIONS variable instead.

Behavior in Actions should stay the same (report log only in CI); local make slow_tests still skips the report log when GITHUB_ACTIONS is unset.

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[bot-ci-comment]

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