agent: Fix duplicate word in agent system prompt template (#49309)

Austin Cummings created 

Release Notes:

- N/A

Change summary

crates/agent/src/templates/system_prompt.hbs | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Detailed changes

crates/agent/src/templates/system_prompt.hbs 🔗 

@@ -48,7 +48,7 @@ The one exception to this is if the user references something you don't know abo
 
 ## Code Block Formatting
 
-Whenever you mention a code block, you MUST use ONLY use the following format:
+Whenever you mention a code block, you MUST ONLY use the following format:
 
 ```path/to/Something.blah#L123-456
 (code goes here)