Use compiler(>=6.1) to gate for the main branch toolchain

[kateinoigakukun]

We used a hack to distinguish the main branch toolchain and 6.0 branch toolchain, but the main branch has been bumped to 6.1, so we can use compiler(>=6.1) to gate for the main branch toolchain.

[github-actions]

Time Change: +218ms (2%)

Total Time: 9,530ms

Test name	Duration	Change
Serialization/JavaScript function call through Wasm import	19ms	+1ms (6%)	🔍
Serialization/JavaScript function call through Wasm import with int	15ms	+1ms (9%)	🔍
Serialization/Swift Int to JavaScript with assignment	339ms	+26ms (7%)	🔍
Serialization/Swift String to JavaScript with assignment	391ms	+22ms (5%)	🔍

View Unchanged

Test name	Duration	Change
Serialization/JavaScript function call from Swift	99ms	+4ms (4%)
Serialization/Swift Int to JavaScript with call	975ms	+41ms (4%)
Serialization/JavaScript Number to Swift Int	315ms	+10ms (3%)
Serialization/Swift String to JavaScript with call	1,026ms	+49ms (4%)
Serialization/JavaScript String to Swift String	3,654ms	+49ms (1%)
Object heap/Increment and decrement RC	2,684ms	+14ms (0%)

View Baselines

Test name	Duration
Serialization/Call JavaScript function directly	3ms
Serialization/Assign JavaScript number directly	3ms
Serialization/Call with JavaScript number directly	3ms
Serialization/Write JavaScript string directly	3ms
Serialization/Call with JavaScript string directly	4ms