CI - IMPROVEMENT - Narrow test triggering to an allowlist of tested paths

The detector matched any .jl file outside a denylist of docs, benchmarks and
regression-harness. That meant new untested Julia triggered a full run unless
someone remembered to extend the denylist: a benchmark, a root-level script,
or a future tools/ directory all ran the suite for nothing.

Replace it with an allowlist of what test/runtests.jl actually exercises:
src/, test/, examples/, Project.toml, and this workflow. Untested code is now
excluded by default rather than by maintenance.

Kept as directory prefixes rather than *.jl: src/ForcingTerms/coil_geometries
holds the .dat coil geometries the coil tests load, and test/test_data holds 28
non-Julia fixtures. Matching only *.jl would skip runs when either changes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019tFBCa5iBXyb7xp8LxqBJx

Author: Claude

.github/workflows/test.yaml

@@ -54,13 +54,15 @@ jobs:
 
           files=$(gh api --paginate "repos/${REPO}/pulls/${PR_NUMBER}/files" --jq '.[].filename')
 
-          # Directories whose Julia sources are not exercised by test/runtests.jl.
-          not_tested='^(docs|benchmarks|regression-harness)/'
-          # Everything the test suite actually reads: sources, tests and their
-          # fixtures, the example decks the tests run end-to-end, and this workflow.
-          tested='(\.jl$|^Project\.toml$|^test/|^examples/|^\.github/workflows/test\.yaml$)'
-
-          relevant=$(printf '%s\n' "$files" | grep -Ev "$not_tested" | grep -E "$tested" || true)
+          # Allowlist of what test/runtests.jl actually exercises: the package
+          # itself, the tests and their fixtures, the example decks the tests run
+          # end-to-end, the dependency set, and this workflow. Anything not listed
+          # here does not trigger a run, so new untested Julia (benchmarks, docs
+          # scripts, a future tools/ directory) is excluded by default rather than
+          # by remembering to exclude it.
+          tested='(^src/|^test/|^examples/|^Project\.toml$|^\.github/workflows/test\.yaml$)'
+
+          relevant=$(printf '%s\n' "$files" | grep -E "$tested" || true)
 
           say "### Julia change detection"
           say ""