Not sure why CI is failing. That should be fixed on master, no?

Master is failing too on AppVeyor:
00:01:58] Running org.antlr.v4.test.runtime.go.TestCompositeLexers
[00:02:03] Tests run: 2, Failures: 2, Errors: 0, Skipped: 0, Time elapsed: 5.118 sec <<< FAILURE! - in org.antlr.v4.test.runtime.go.TestCompositeLexers
[00:02:03] testOneGo:LexerDelegatorRuleOverridesDelegate Time elapsed: 1.369 sec <<< FAILURE!
[00:02:03] junit.framework.AssertionFailedError:
[00:02:03] [Go:LexerDelegatorRuleOverridesDelegate] Parse output is incorrect: expectedOutput:<M.A
[00:02:03] [@0,0:1='ab',<1>,1:0]
[00:02:03] [@1,2:1='',<-1>,1:2]
[00:02:03] >; actualOutput:<>; expectedParseErrors:<>; actualParseErrors:<parser\m_lexer.go:9:2: no required module provides package github.com/antlr/antlr4/runtime/Go/antlr: go.mod file not found in current directory or any parent directory; see 'go help modules'
[00:02:03] >; expectedToolErrors:<>; actualToolErrors:<>.

-> thousands of the above

I think, and this might be wrong, but I think that the problem is that the testing environment doesn't set up the main module, i.e., the package of the tests isn't a part of a module, so trying to use modules makes the go tool complain. I think I overlooked that part in my own PR