ci: name the encoding the check reads its sources in

Python opens a file with the platform's default encoding, which on the Windows
runner is cp1252, and these sources are UTF-8:

    UnicodeDecodeError: 'charmap' codec can't decode byte 0x90 in position 90

A check that reads source files must say what they are encoded in, or it reports
on the runner's locale rather than on the sources. The byte it stopped at is in a
comment marker, so the check would have passed on a repository whose comments
happened to be ASCII and failed on this one --- which is the least useful place
for a difference to appear.

Both reads name utf-8. Rehearsed locally under cp1252: 42 declared, 49 exported,
none missing.

Author: speak-agent

.github/workflows/ci.yml

@@ -182,11 +182,18 @@ jobs:
         run: |
           python3 - <<'PY'
           import glob, os, re, sys
+          # ⚠️ THE ENCODING IS NAMED. Python opens a file with the platform's
+          # default, which on this runner is cp1252, and these sources are UTF-8:
+          #
+          #     UnicodeDecodeError: 'charmap' codec can't decode byte 0x90
+          #
+          # A check that reads source files must say what they are encoded in, or
+          # it reports on the runner's locale.
           declared = set(re.findall(r'OKW_IMPORT\s+\w+\s+OKW_API\s+(\w+)\s*\(',
-                                    open("src/win32.h").read()))
+                                    open("src/win32.h", encoding="utf-8").read()))
           exported = set()
           for f in glob.glob("port/*.def"):
-              body = open(f).read().split("EXPORTS", 1)
+              body = open(f, encoding="utf-8").read().split("EXPORTS", 1)
               if len(body) < 2: continue
               exported |= {l.strip() for l in body[1].split("\n")
                            if l.strip() and not l.lstrip().startswith(';')}