Assert the parser is at augmented assign token (#10269)

## Summary

This PR updates fixes one of the `FIXME` comment to assert that the
parser is at one of the possible augmented assignment token when parsing
an augmented assignment statement.

## Test Plan

1. Add valid test cases for all the possible augmented assignment tokens
2. Add invalid test cases similar to assignment statement

crates/ruff_python_parser/resources/invalid/statements/invalid_assignment_targets.py

@@ -27,17 +27,6 @@ await x = 42
 a < b < c = 42
 foo() = 42
 
-# N.B. It looks like the parser can't generate a top-level
-# FormattedValue, where as the official Python AST permits
-# representing a single f-string containing just a variable as a
-# FormattedValue directly.
-#
-# Bottom line is that because of this, this test is (at present)
-# duplicative with the `fstring` test. That is, in theory these tests
-# could fail independently, but in practice their failure or success
-# is coupled.
-#
-# See: https://docs.python.org/3/library/ast.html#ast.FormattedValue
 f"{quux}" = 42
 f"{foo} and {bar}" = 42
 

crates/ruff_python_parser/resources/invalid/statements/invalid_augmented_assignment_target.py

@@ -0,0 +1,34 @@
+# This is similar to `./invalid_assignment_targets.py`, but for augmented
+# assignment targets.
+
+x or y += 42
+(x := 5) += 42
+x + y += 42
+-x += 42
+(lambda _: 1) += 42
+a if b else c += 42
+{"a": 5} += 42
+{a} += 42
+[x for x in xs] += 42
+{x for x in xs} += 42
+{x: x * 2 for x in xs} += 42
+(x for x in xs) += 42
+await x += 42
+(yield x) += 42
+(yield from xs) += 42
+a < b < c += 42
+foo() += 42
+
+f"{quux}" += 42
+f"{foo} and {bar}" += 42
+
+"foo" += 42
+b"foo" += 42
+123 += 42
+True += 42
+None += 42
+... += 42
+*foo() += 42
+[x, foo(), y] += [42, 42, 42]
+[[a, b], [[42]], d] += [[1, 2], [[3]], 4]
+(x, foo(), y) += (42, 42, 42)

crates/ruff_python_parser/resources/valid/statement/augmented_assignment.py

@@ -1,3 +1,18 @@
 x += 1
 x.y += (1, 2, 3)
 x[y] += (1, 2, 3)
+
+# All possible augmented assignment tokens
+x += 1
+x -= 1
+x *= 1
+x /= 1
+x //= 1
+x %= 1
+x **= 1
+x &= 1
+x |= 1
+x ^= 1
+x <<= 1
+x >>= 1
+x @= 1