Don't use the tool cache on GitHub-hosted runners by default

This introduces performance problems due to deficiencies in the
filesystem layout of GitHub-hosted runners; see #34. The tool cache
isn't very useful on such runners anyway, but I've added an option to
override the default.

Also add some more logging (related: #45).

Resolves: #34

Author: github-actions[bot]

common.js

@@ -32,7 +32,7 @@ async function getVersion() {
         return _cached_version;
       }
 
-      // Else, look for `mach_zig_version` first
+      // Else, look for `minimum_zig_version`
       match = MINIMUM_ZIG_VERSION_REGEX.exec(zon);
       if (match !== null) {
         _cached_version = match[1];