main: rename goroutine tests

While LLVM coroutines are one implementation of goroutines, it is not
the only one. Therefore, rename the tests to 'goroutines' to better
describe what they're for.

testdata/goroutines.txt

@@ -0,0 +1,22 @@
+main 1
+sub 1
+main 2
+sub 2
+main 3
+wait:
+  wait start
+  wait end
+end waiting
+value produced after some time: 42
+non-blocking goroutine
+done with non-blocking goroutine
+async interface method call
+slept inside func pointer 8
+slept inside closure, with value: 20 8
+closure go call result: 1
+pre-acquired mutex
+releasing mutex
+acquired mutex from goroutine
+released mutex from goroutine
+re-acquired mutex
+done