fix: load config defaults if not specified in existing config #3154

Job	Run time
build (1.20.x, GOARCH=amd64 GOOS=linux, gno)	29s
build (1.20.x, GOARCH=wasm GOOS=js, gno)	45s
build (1.21.x, GOARCH=amd64 GOOS=linux, gno)	28s
test (1.20.x, _test.cmd)	1m 18s
build (1.21.x, GOARCH=wasm GOOS=js, gno)	26s
test (1.20.x, _test.pkg)	1m 26s
test (1.20.x, _test.gnolang.native)	47s
test (1.20.x, _test.gnolang.stdlibs)	1m 9s
test (1.20.x, _test.gnolang.realm)	45s
test (1.20.x, _test.gnolang.pkg0)	1m 56s
test (1.20.x, _test.gnolang.pkg1)	6m 26s
test (1.20.x, _test.gnolang.pkg2)	4m 19s
test (1.20.x, _test.gnolang.other)	42s
test (1.21.x, _test.cmd)	1m 23s
test (1.21.x, _test.pkg)	52s
test (1.21.x, _test.gnolang.native)	38s
test (1.21.x, _test.gnolang.stdlibs)	1m 7s
test (1.21.x, _test.gnolang.realm)	50s
test (1.21.x, _test.gnolang.pkg0)	1m 51s
test (1.21.x, _test.gnolang.pkg1)	6m 17s
test (1.21.x, _test.gnolang.pkg2)	4m 15s
test (1.21.x, _test.gnolang.other)	44s
upload-coverage	19s
	39m 12s

Provide feedback