[FURB156] Do not consider docstring(s) (#16391)

Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_linter/resources/test/fixtures/refurb/FURB156.py

@@ -27,8 +27,26 @@ _ = (
     # with comment
 ).capitalize()
 
+# example with augmented assignment
+_ += "0123456789"
+
 # OK
 
 _ = "1234567890"
 _ = "1234"
 _ = "12" in "12345670"
+
+
+# No errors as the string is considered as a docstring
+class C:
+    "01234567"
+
+
+class C:
+    def method(self):
+        "01234567"
+
+
+def function():
+    """01234567"""
+

crates/ruff_linter/src/rules/refurb/rules/hardcoded_string_charset.rs

@@ -46,6 +46,11 @@ impl AlwaysFixableViolation for HardcodedStringCharset {
 
 /// FURB156
 pub(crate) fn hardcoded_string_charset_literal(checker: &Checker, expr: &ExprStringLiteral) {
+    // if the string literal is a docstring, the rule is not applied
+    if checker.semantic().in_pep_257_docstring() {
+        return;
+    }
+
     if let Some(charset) = check_charset_exact(expr.value.to_str().as_bytes()) {
         push_diagnostic(checker, expr.range, charset);
     }

crates/ruff_linter/src/rules/refurb/snapshots/ruff_linter__rules__refurb__tests__FURB156_FURB156.py.snap

@@ -331,4 +331,30 @@ FURB156.py:26:5: FURB156 [*] Use of hardcoded string charset
    27 |+    string.digits
 27 28 |     # with comment
 28 29 | ).capitalize()
-29 30 |
+29 30 | 
+
+FURB156.py:31:6: FURB156 [*] Use of hardcoded string charset
+   |
+30 | # example with augmented assignment
+31 | _ += "0123456789"
+   |      ^^^^^^^^^^^^ FURB156
+32 |
+33 | # OK
+   |
+   = help: Replace hardcoded charset with `string.digits`
+
+ℹ Safe fix
+1  1  | # Errors
+   2  |+import string
+2  3  | 
+3  4  | _ = "0123456789"
+4  5  | _ = "01234567"
+--------------------------------------------------------------------------------
+28 29 | ).capitalize()
+29 30 | 
+30 31 | # example with augmented assignment
+31    |-_ += "0123456789"
+   32 |+_ += string.digits
+32 33 | 
+33 34 | # OK
+34 35 |