fix(go): preserve failing test location context

[em0t]

Summary

• keep file-and-line failure locations in compact rtk go test output instead of dropping them when they do not contain keywords
• preserve the first follow-up context line after a foo_test.go:42: location entry so assertion messages remain readable
• add regression coverage for failed test output that uses a location line followed by an indented explanation

Minimal Case

Raw

foo_test.go:42:
    values differ after normalization

Previous RTK

foo (0 passed, 1 failed)
  [FAIL] TestFail

This PR

foo (0 passed, 1 failed)
  [FAIL] TestFail
     foo_test.go:42:
     values differ after normalization

Testing

• cargo fmt --all
• cargo clippy --all-targets
• cargo test --all

Notes

• cargo clippy --all-targets still reports pre-existing warnings outside this change set

[CLAassistant]

All committers have signed the CLA.

[em0t]

Could a maintainer please approve and run workflows so CI can start for review?

[aeppling]

Valid and clean, thanks for contributing