Fix panic when trying to set subkey for a value that's not a table

Would panic for inline tables; regression added in 4223137.

Fixes #403

parse.go

@@ -485,7 +485,10 @@ func (p *parser) valueInlineTable(it item, parentIsArray bool) (any, tomlType) {
 				h = make(map[string]any)
 				hash[c] = h
 			}
-			hash = h.(map[string]any)
+			hash, ok = h.(map[string]any)
+			if !ok {
+				p.panicf("%q is not a table", p.context)
+			}
 		}
 		hash[p.currentKey] = val
 

toml_test.go

@@ -313,9 +313,6 @@ func runTomlTest(t *testing.T, includeNext bool, wantFail ...string) {
 			Parser:   parser{},
 			RunTests: runTests,
 			SkipTests: []string{
-				// TODO: https://github.com/BurntSushi/toml/issues/403
-				"invalid/inline-table/overwrite-10",
-
 				// These tests are fine, just doesn't deal well with empty output.
 				"valid/comment/noeol",
 				"valid/comment/nonascii",