Fix flaky test case in CacheStoreBehavior

[ghousemohamed]

Summary

In a PR I had raised earlier, one of the test cases in ActiveSupport was failing, even though the PR did not touch any piece of code related to ActiveSupport. Upon closer inspection, I found that this is the test case that was failing:

PR: #44385
Ref: https://buildkite.com/rails/rails/builds/84552#2c168cf4-a799-4b58-a1ec-cc3032854894/1183-1205

rails/activesupport/test/cache/behaviors/cache_store_behavior.rb

Lines 408 to 412 in b961af3

	def test_keys_are_case_sensitive
	key = SecureRandom.alphanumeric
	@cache.write(key, "bar")
	assert_nil @cache.read(key.upcase)
	end

Since SecureRandom.alphanumeric returns a string in which the alphabets are not guaranteed to be all be lowercase, it can possibly return a string with only uppercase letters and numbers present in it. And since in this test case we are testing for case sensitivity, in the rare occasion a string is returned with only uppercase letters, this test case will fail.

This PR intends to account for this edge case.

Thanks!

Other Information

[nvasilevski]

Good catch!