test: mocks and snapshots for all exec() calls (#5089)

lib/manager/composer/artifacts.ts

lib/manager/gomod/artifacts.ts

lib/manager/pip_setup/extract.ts

test/execUtil.ts

test/manager/bundler/__snapshots__/artifacts.spec.ts.snap

test/manager/bundler/artifacts.spec.ts

test/manager/cargo/__snapshots__/artifacts.spec.ts.snap

test/manager/cargo/artifacts.spec.ts

test/manager/composer/__snapshots__/artifacts.spec.ts.snap

test/manager/composer/artifacts.spec.ts

test/manager/gomod/__snapshots__/artifacts.spec.ts.snap

test/manager/gomod/artifacts.spec.ts

test/manager/gradle/__snapshots__/index.spec.ts.snap

test/manager/gradle/index.spec.ts

test/manager/mix/__snapshots__/artifacts.spec.ts.snap

test/manager/mix/artifacts.spec.ts

test/manager/pip_setup/__snapshots__/extract.spec.ts.snap

test/manager/pip_setup/__snapshots__/index.spec.ts.snap

test/manager/pip_setup/extract.spec.ts

test/manager/pip_setup/index.spec.ts