Fix variable naming in `examples/e14_slash_commands` example (#3443) #6396

Job	Run time
Test (nightly)	2m 5s
Build docs	53s
Check minimal versions	59s
Test (beta)	2m 6s
Examples	4m 2s
Test (no default features)	50s
Test (no gateway)	1m 30s
Test (native-tls)	1m 58s
Test (chrono, chrono)	52s
Test (Windows)	5m 37s
Test (simd-json)	2m 4s
Test (unstable API + typesize, default unstable_discord_api typesize, true)	1m 23s
Test (unstable Discord API features)	2m 10s
Test (stable)	2m 2s
MSRV	1m 1s
Test (builder without model, builder, true)	27s
Test (macOS)	3m 50s
Test (no cache)	1m 55s
Test (unstable Discord API (no default features), unstable_discord_api, true)	36s
	36m 20s

Provide feedback