only load env_file after services have been selected

[ndeloof]

What I did
resolve env_file after active services have been selected, so we don't read (potentially missing) env_file for inactive ones

Related issue
fixes #8713
requires compose-spec/compose-go#751

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PR Overview

This PR ensures that env_file entries are only loaded for active services, preventing potential errors when an env_file does not exist for inactive services.

• Adds a new compose file fixture with two services where only one references an env_file.
• Introduces a new end-to-end test to confirm that missing env_file for inactive services does not trigger an error.
• Adjusts the project environment resolution logic in cmd/compose/compose.go to resolve env_file only after services selection.

Reviewed Changes

File	Description
pkg/e2e/fixtures/env_file/compose.yaml	New test fixture with two services, one specifying a missing env_file
pkg/e2e/env_file_test.go	Added test to verify that env_file for inactive services is not loaded
cmd/compose/compose.go	Updated environment resolution order to resolve after services are selected

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

pkg/e2e/env_file_test.go:38

• Consider adding an assertion to verify that the missing env_file for serviceB is not processed, ensuring the test precisely validates that inactive services do not trigger an env_file load error.

    c.RunDockerComposeCmd(t, "-f", "./fixtures/env_file/compose.yaml", "up", "-d", "serviceA")

[glours]

LGTM 👍