fix typo (#58)

Author: luckrnx09

docs/arithmetic-operation.md

@@ -113,7 +113,7 @@ print("Updated num2 after decrement:", num2)
 | Remainder | `%` | `%` |
 | Exponentiation | `**` | `**` |
 | Increment | `++` <br /> `+=1` | `+= 1` |
-| Decrement | `--` <br/> `+=1` | `-= 1` |
+| Decrement | `--` <br/> `-=1` | `-= 1` |
 
 :::danger
 In Python, arithmetic operations can only be performed between **compatible** data types. For example, the result of a calculation between a floating-point number and an integer will be a floating-point number. However, performing arithmetic operations between a string and a number will result in an error. To perform arithmetic operations between a number and a string, one of them must be converted to the appropriate data type.

i18n/zh-cn/docusaurus-plugin-content-docs/current/arithmetic-operation.md

@@ -113,7 +113,7 @@ print("自减后的 num2：", num2)
 | 取余 | `%` | `%` |
 | 指数运算 | `**` | `**` |
 | 自增 | `++` <br /> `+=1` | `+= 1` |
-| 自减 | `--` <br/> `+=1` | `-= 1` |
+| 自减 | `--` <br/> `-=1` | `-= 1` |
 
 :::danger
 在 Python 中，只有 **兼容的** 数据类型之间才能进行运算，比如浮点数和整数运算的结果为浮点数，而字符串和数字进行运算会抛出异常。如要对数字和字符串进行运算，需先对其中一进行类型转换。