Coerce CI auto_retry max value to an integer

Users that used a string (e.g. `'3'` instead of 3) would encounter
an exception such as:

```
ArgumentError: comparison of String with 0 failed
```

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/233035

lib/gitlab/ci/build/auto_retry.rb

@@ -30,7 +30,7 @@ class Gitlab::Ci::Build::AutoRetry
   end
 
   def options_retry_max
-    options_retry[:max] if retry_on_reason_or_always?
+    Integer(options_retry[:max], exception: false) if retry_on_reason_or_always?
   end
 
   def options_retry_when

spec/lib/gitlab/ci/build/auto_retry_spec.rb

@@ -16,6 +16,7 @@ RSpec.describe Gitlab::Ci::Build::AutoRetry do
       "retries are disabled" | 0 | { max: 0 } | nil | false
       "max equals count" | 2 | { max: 2 } | nil | false
       "max is higher than count" | 1 | { max: 2 } | nil | true
+      "max is a string" | 1 | { max: '2' } | nil | true
       "matching failure reason" | 0 | { when: %w[api_failure], max: 2 } | :api_failure | true
       "not matching with always" | 0 | { when: %w[always], max: 2 } | :api_failure | true
       "not matching reason" | 0 | { when: %w[script_error], max: 2 } | :api_failure | false