Adjust test log output to display diffs only for failing test results

[eysk-io]

Adjusted test log output to display diffs only when comparing failed test results with expected test results. For example, compilation errors will no longer compare expected results with error logs.

Example compilation error log BEFORE change:

Compiling queries in <path-to-test>.
[1/1 comp 5s] FAILED(COMPILATION) <path-to-test>
0 tests passed; 1 tests failed:
  FAILED: <path-to-test>

errored: <path-to-test>
--- expected
+++ actual
@@ -1,1 +1,1 @@
-| main.go:15:41:15:52 | call to len |
+ERROR: Could not resolve predicate length/0 (<path-to-test>)

Same error AFTER change:

Compiling queries in <path-to-test>.
[1/1 comp 5.5s] FAILED(COMPILATION) <path-to-test>
0 tests passed; 1 tests failed:
  FAILED: <path-to-test>

compilation error: <path-to-test>
ERROR: Could not resolve predicate length/0

Closes #819.

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [n/a] @github/docs-content-codeql has been cc'd in all issues for UI or other user-facing changes made by this pull request.

[aeisenberg]

This is looking great. Thanks for the contribution.