Fix potential crash in show-commit

What does this MR do?

In development mode when lazy loading classes, this caused Rails to look up Environments on Projects, where it is not defined, causing a crash:

NameError at /gpt/large_projects/gitlabhq1/-/commit/871d01c193bbc52802294cbf7e32234e09d3a199
uninitialized constant Projects::Environments::EnvironmentsByDeploymentsFinder

Explicitly forcing a top-level lookup fixes this. I am unsure how to add test coverage for this.

Does this MR meet the acceptance criteria?

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