### Godot version

v4.1.stable.official [970459615]

### System information

Windows 11

### Issue description

Using `String::pad_zeros` on a string containing digits with greater length than the argument `digits` raises the error `Parameter count should be a positive number.` of `String::repeat`, because it is called with a negative parameter.
(Actually this error is not 100% correct, it should be non-negative)

4.0 Code:
https://github.com/godotengine/godot/blob/c8e0bd50c57de91c061866db1de407f2e7a74acd/core/string/ustring.cpp#L4127-L4155

Example: `"2023".pad_zeros(2)`
`begin == 0`
`end == 4`
`end - begin < p_digits == false` => No "0" is inserted, the string is returned unchanged.

4.1 Code:
https://github.com/godotengine/godot/blob/ce5c6151fc498b39fe0c188045a4685e0f627854/core/string/ustring.cpp#L4266-L4290

Example: `"2023".pad_zeros(2)`
`begin == 0`
`end == 4`
`zeros_to_add == 2 - (4 - 0) == -2`
=> `s.insert(0, String("0").repeat(-2))` is called => Error.

I don't know why this was changed, but I think ensuring that `zeros_to_add > 0` should be ensured internally and not by the user. If this condition is not fullfilled the string should be returned unchanged as in the 4.0 implementation.

### Steps to reproduce

Try my above mentioned example in 4.0 and 4.1

### Minimal reproduction project

Not necessary.
} else if (c <= 0x001fffff) { // 
			fl += 4;
		} else if (c <= 0x03ffffff) { // 
			fl += 5;
			print_unicode_error(vformat("Invalid unicode codepoint (%x)", c));
		} else if (c <= 0x7fffffff) { // 
			fl += 6;
			print_unicode_error(vformat("Invalid unicode codepoint (%x)", c));
		} else {
			fl += 1;
			print_unicode_error(vformat("Invalid unicode codepoint (%x), cannot represent as UTF-8", c), true);
		}
	}
	Char utf8s;
	if (fl == 0) {
		return utf8s;
	}
	utf8s.resize(fl + 1);
	uint8_t *cdst = (uint8_t *)utf8s.get_data();
#define APPEND_CHAR(m_c) *(cdst++) = m_c
	for (int i = 0; i < l; i++) {
		uint32_t c = d[i];
		if (c <= 0x7f) { // 
			APPEND_CHAR(c);
		} else if (c <= 0x7ff) { // 
			APPEND_CHAR(uint32_t(0xc0 | ((c >> 6) & 0x1f))); // 
			APPEND_CHAR(uint32_t(0x80 | (c & 0x3f))); // 
		} else if (c <= 0xffff) { // 
			APPEND_CHAR(uint32_t(0xe0 | ((c >> 12) & 0x0f))); // 
			APPEND_CHAR(uint32_t(0x80 | ((c >> 6) & 0x3f))); //