Adjust self-analysis for the more precise foreach-body narrowing

With the foreach body now narrowing the iterated expression to non-empty
even when polluteScopeWithAlwaysIterableForeach is off, PHPStan's own
strict-rules self-analysis proves two facts it previously left uncertain:

- UnionType::accepts() reuses $i as the value variable of a second foreach
  after it was the key variable of an earlier one; the reused name now
  reads as a foreach.valueOverwrite. Rename the second loop's variable.

- ConstantArrayType::isSuperTypeOf() destructures $this->unsealed /
  $type->unsealed (typed array{Type, Type}|null) in branches guarded by a
  separate unsealedness check that PHPStan cannot connect to the property.
  Read the property into a local and throw ShouldNotHappenException on null,
  matching the file's existing impossible-state style.

Both are genuine facts surfaced by the more precise analysis, independent of
the flag; no behaviour changes.

Author: zonuexe

src/Type/Constant/ConstantArrayType.php

@@ -811,7 +811,11 @@ public function isSuperTypeOf(Type $type): IsSuperTypeOfResult
 						continue;
 					}
 
-					[$thisUnsealedKey, $thisUnsealedValue] = $this->unsealed;
+					$thisUnsealed = $this->unsealed;
+					if ($thisUnsealed === null) {
+						throw new ShouldNotHappenException();
+					}
+					[$thisUnsealedKey, $thisUnsealedValue] = $thisUnsealed;
 					$keyCheck = $thisUnsealedKey->isSuperTypeOf($typeKey);
 					if ($keyCheck->no()) {
 						if ($type->isOptionalKey($i)) {
@@ -835,8 +839,13 @@ public function isSuperTypeOf(Type $type): IsSuperTypeOfResult
 					if ($thisUnsealedness->no()) {
 						$results[] = IsSuperTypeOfResult::createMaybe();
 					} else {
-						[$thisUnsealedKey, $thisUnsealedValue] = $this->unsealed;
-						[$typeUnsealedKey, $typeUnsealedValue] = $type->unsealed;
+						$thisUnsealed = $this->unsealed;
+						$typeUnsealed = $type->unsealed;
+						if ($thisUnsealed === null || $typeUnsealed === null) {
+							throw new ShouldNotHappenException();
+						}
+						[$thisUnsealedKey, $thisUnsealedValue] = $thisUnsealed;
+						[$typeUnsealedKey, $typeUnsealedValue] = $typeUnsealed;
 						$results[] = $thisUnsealedKey->isSuperTypeOf($typeUnsealedKey);
 						$results[] = $thisUnsealedValue->isSuperTypeOf($typeUnsealedValue);
 					}

src/Type/UnionType.php

@@ -239,9 +239,9 @@ public function accepts(Type $type, bool $strictTypes): AcceptsResult
 		}
 		if ($commonReasons !== null && count($commonReasons) > 0) {
 			$decorated = [];
-			foreach (array_keys($innerAccepts) as $i) {
+			foreach (array_keys($innerAccepts) as $innerAcceptsIndex) {
 				foreach ($commonReasons as $reason) {
-					$decorated[] = sprintf('Type #%d from the union: %s', $i + 1, $reason);
+					$decorated[] = sprintf('Type #%d from the union: %s', $innerAcceptsIndex + 1, $reason);
 				}
 			}
 			$result = new AcceptsResult($result->result, $decorated);