CI: Pin Node.js 18 to avoid npm 10 on 32-bit Windows

npm 10 seems to be opening thousands of network connections,
leading to resource starvation in Node.js 18. This does not
appear to impact Node.js 20.

.github/workflows/ci.yml

@@ -47,7 +47,7 @@ jobs:
             platform: darwin-x64
           - os: windows-2019
             nodejs_arch: x86
-            nodejs_version: "^18.17.0"
+            nodejs_version: "18.18.2" # pinned to avoid 18.19.0 and npm 10
             nodejs_version_major: 18
             platform: win32-ia32
             prebuild: true