`cache-hit` is `false` on case-insensitive cache key match

[kbriggs]

Description

Some self-hosted (or otherwise non-github-hosted) runners are non-case-preserving for cache keys. In such configurations, the cache-hit output variable is currently set to false instead of true, even though the case provider did find an exact match (albeit not a case-sensitive one).

For example, in my codeberg-hosted action:

Cache Configuration
Cache Provider:
    github
…
Restore Key:
    v0-rust-cargodeps-Linux-x64-345d6b90
Cache Key:
    v0-rust-cargodeps-Linux-x64-345d6b90-10ea9ea9
.. Prefix:
  - v0-rust-cargodeps-Linux-x64
.. Environment considered:
  - Rust Version: 1.92.0 x86_64-unknown-linux-gnu (ded5c06cf21d2b93bffd5d884aa6e96934ee4234)
…
... Restoring cache ...
Cache Size: ~157 MB (165006101 B)
[command]/usr/bin/tar -xf /tmp/d6553c1f-2a84-47f5-b618-d056b98a1519/cache.tzst -P -C /workspace/kbriggs/airtouch5 --use-compress-program unzstd
Cache restored successfully
Restored from cache key "v0-rust-cargodeps-linux-x64-345d6b90-10ea9ea9" full match: false.

(note the capital L in the OS name in the generated cache key, verses the lowercase l in the returned match)

Expected behaviour

cache-hit is set to true when the found cache key differs only in case, but is otherwise identical.

Prior art

• A similar issue was reported against the ruby/setup-ruby action, Cache keys are treated as case-sensitive, but case is not preserved in all environments ruby/setup-ruby#659, when using the self-hosted act runner, which coerces cache keys to lowercase.

• The actions/cache action itself uses a case-insensitive match:

  export function isExactKeyMatch(key: string, cacheKey?: string): boolean {
      return !!(
          cacheKey &&
          cacheKey.localeCompare(key, undefined, {
              sensitivity: "accent"
          }) === 0
      );
  }