Fix index out of bound for Dagger compute inputs + add tests ["input-dir", "input-git", input-string"]

Signed-off-by: Guillaume de Rouville <guillaume.derouville@gmail.com>

tests/compute.bats

@@ -65,6 +65,18 @@ setup() {
     run "$DAGGER" compute --input-string 'in=foobar' "$TESTDIR"/compute/input/default
     assert_success
     assert_line '{"in":"foobar","test":"received: foobar"}'
+    
+    run "$DAGGER" compute --input-string=foobar "$TESTDIR"/compute/input/default
+    assert_failure
+    assert_output --partial 'failed to parse input: input-string'
+    
+    run "$DAGGER" compute --input-dir=foobar "$TESTDIR"/compute/input/default
+    assert_failure
+    assert_output --partial 'failed to parse input: input-dir'
+
+    run "$DAGGER" compute --input-git=foobar "$TESTDIR"/compute/input/default
+    assert_failure
+    assert_output --partial 'failed to parse input: input-git'
 }
 
 @test "compute: secrets" {