docs(README): Fix date format from 12h to 24h in schedule pattern

hh represents 12h format from 01 to 12 which is probably not suitable
for date tags.
The pattern example in the table below uses the 24h format HH, so this
makes the document consistent.

Signed-off-by: motoki317 <[email protected]>

Author: motoki317

README.md

@@ -464,7 +464,7 @@ tags: |
   # handlebars
   type=schedule,pattern={{date 'YYYYMMDD'}}
   # handlebars with timezone
-  type=schedule,pattern={{date 'YYYYMMDD-hhmmss' tz='Asia/Tokyo'}}
+  type=schedule,pattern={{date 'YYYYMMDD-HHmmss' tz='Asia/Tokyo'}}
 ```
 
 Will be used on [schedule event](https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#schedule).