Clarify that the `restore-keys` input is a string in the docs (#1434)

* Fix Description for restore-keys at Readme

As previously the restore-keys were defined as an ordered lists which is
wrong as per the issue description where the actual format is a
multi-line string with one key per line.

* Added a space between the sentence of restore-keys description

While at the PR review it's been identified there's a need for a space
between the sentence

	```
	An ordered multiline string listing the prefix-matched keys,that are
	used for restoring stale cache if no cache hit occurred for key.
	```

where it's written as "prefix-matched keys,that are" this commit will
address the review comment and introduce a space between
"prefix-matched keys, that are" and change the sentence to

	```
	An ordered multiline string listing the prefix-matched keys, that are
        used for restoring stale cache if no cache hit occurred for key.
	```

* Change restore-keys description at cache/restore/action.yml and cache/action.yml

README.md

@@ -54,7 +54,7 @@ If you are using a `self-hosted` Windows runner, `GNU tar` and `zstd` are requir
 
 * `key` - An explicit key for a cache entry. See [creating a cache key](#creating-a-cache-key).
 * `path` - A list of files, directories, and wildcard patterns to cache and restore. See [`@actions/glob`](https://github.com/actions/toolkit/tree/main/packages/glob) for supported patterns.
-* `restore-keys` - An ordered list of prefix-matched keys to use for restoring stale cache if no cache hit occurred for key.
+* `restore-keys` - An ordered multiline string listing the prefix-matched keys, that are used for restoring stale cache if no cache hit occurred for key.
 * `enableCrossOsArchive` - An optional boolean when enabled, allows Windows runners to save or restore caches that can be restored or saved respectively on other platforms. Default: `false`
 * `fail-on-cache-miss` - Fail the workflow if cache entry is not found. Default: `false`
 * `lookup-only` - If true, only checks if cache entry exists and skips download. Does not change save cache behavior. Default: `false`

action.yml

@@ -9,7 +9,7 @@ inputs:
     description: 'An explicit key for restoring and saving the cache'
     required: true
   restore-keys:
-    description: 'An ordered list of keys to use for restoring stale cache if no cache hit occurred for key. Note `cache-hit` returns false in this case.'
+    description: 'An ordered multiline string listing the prefix-matched keys, that are used for restoring stale cache if no cache hit occurred for key. Note `cache-hit` returns false in this case.'
     required: false
   upload-chunk-size:
     description: 'The chunk size used to split up large files during upload, in bytes'

restore/action.yml

@@ -9,7 +9,7 @@ inputs:
     description: 'An explicit key for restoring the cache'
     required: true
   restore-keys:
-    description: 'An ordered list of keys to use for restoring stale cache if no cache hit occurred for key. Note `cache-hit` returns false in this case.'
+    description: 'An ordered multiline string listing the prefix-matched keys, that are used for restoring stale cache if no cache hit occurred for key. Note `cache-hit` returns false in this case.'
     required: false
   enableCrossOsArchive:
     description: 'An optional boolean when enabled, allows windows runners to restore caches that were saved on other platforms'