Add skip_fetch input option

This new option will allow users to skip the execution of `git fetch` if it has a negative impact in their workflows.

In a future PR I will probably remove the call to git-fetch interely. It was added in #108 in relation to a problem with slashes in branch names. That problem wasn't properly fixed though.

tests/git-auto-commit.bats

@@ -21,6 +21,7 @@ setup() {
     export INPUT_TAGGING_MESSAGE=""
     export INPUT_PUSH_OPTIONS=""
     export INPUT_SKIP_DIRTY_CHECK=false
+    export INPUT_SKIP_FETCH=false
 
     # Configure Git
     if [[ -z $(git config user.name) ]]; then
@@ -297,3 +298,16 @@ git_auto_commit() {
     run git ls-remote --tags --refs
     assert_output --partial refs/tags/v2.0.0
 }
+
+@test "If SKIP_FETCH is true git-fetch will not be called" {
+
+    touch "${FAKE_LOCAL_REPOSITORY}"/new-file-{1,2,3}.txt
+
+    INPUT_SKIP_FETCH=true
+
+    run git_auto_commit
+
+    assert_success
+
+    assert_line "::debug::git-fetch has not been executed"
+}