get-ci-matrix.py: ignore IMPLS.yml and Makefile.impls

This isn't a perfect solution because if somebody pushes a new
implementation and then later pushes the updates to these files, it
probably won't trigger any implementations. However, the workflow can
always be manually triggered for a specific implementation and branch so
that's probably okay. At least this way, the addition of a new
implementation won't always trigger every other implementation to be
tested.

get-ci-matrix.py

@@ -7,7 +7,7 @@
 import yaml
 
 IMPLS_FILE = "IMPLS.yml"
-RE_IGNORE = re.compile(r'(^LICENSE$|^README.md$|^docs/|^process/)')
+RE_IGNORE = re.compile(r'(^LICENSE$|^README.md$|^docs/|^process/|^IMPLS.yml$|^Makefile.impls$)')
 RE_IMPL = re.compile(r'^impls/(?!lib|tests)([^/]*)/')
 
 OVERRIDE_IMPLS = os.environ.get('OVERRIDE_IMPLS', '').split()
@@ -23,7 +23,7 @@ def impl_text(impl):
     return s
 
 all_changes = sys.argv[1:]
-# code changes that are not just to docs
+# code changes that are not just to docs or implementation lists
 code_changes = set([c for c in all_changes if not RE_IGNORE.search(c)])
 # actual changes to implementations
 impl_changes = set([c for c in all_changes if RE_IMPL.search(c)])