fix: preserve equals in extra environment values

[imshunsuke]

Summary

• Preserve = characters after the first separator in the space-separated extra_env_vars fallback parser.
• Add regression coverage to the always-on CPU test matrix.

Problem

_parse_extra_env_vars split each assignment on every = and then kept only the second component. For example:

TOKEN=abc== END=ok

was parsed as:

{"TOKEN": "abc", "END": "ok"}

This corrupts padded or otherwise =-containing environment values.

Change

Use split("=", 1) so only the key/value separator is consumed. JSON input handling and the existing fallback tokenization remain unchanged.

The new zero-GPU regression test is registered in the workflow template, and the generated workflow is updated with it.

Testing

• tests/utils/test_command_utils.py: 1 passed
• pre-commit run --all-files
• Confirmed the generated pr-test.yml matches pr-test.yml.j2
• git diff --check