Fix E203 false positive for slices in format strings (astral-sh#10280)

## Summary

The code later in this file that checks for slices relies on the stack
of brackets to determine the position. I'm not sure why format strings
were being excluded from this, but the tests still pass with these match
guards removed.

Closes astral-sh#10278

## Test Plan

~Still needs a test.~ Test case added for this example.

crates/ruff_linter/resources/test/fixtures/pycodestyle/E20.py

@@ -153,3 +153,9 @@
 
 #: E203:1:13
 ham[lower + 1  :, "columnname"]
+
+#: Okay
+f"{ham[lower +1 :, "columnname"]}"
+
+#: E203:1:13
+f"{ham[lower + 1  :, "columnname"]}"

crates/ruff_linter/src/rules/pycodestyle/rules/logical_lines/extraneous_whitespace.rs

@@ -137,16 +137,16 @@ pub(crate) fn extraneous_whitespace(line: &LogicalLine, context: &mut LogicalLin
         match kind {
             TokenKind::FStringStart => fstrings += 1,
             TokenKind::FStringEnd => fstrings = fstrings.saturating_sub(1),
-            TokenKind::Lsqb if fstrings == 0 => {
+            TokenKind::Lsqb => {
                 brackets.push(kind);
             }
-            TokenKind::Rsqb if fstrings == 0 => {
+            TokenKind::Rsqb => {
                 brackets.pop();
             }
-            TokenKind::Lbrace if fstrings == 0 => {
+            TokenKind::Lbrace => {
                 brackets.push(kind);
             }
-            TokenKind::Rbrace if fstrings == 0 => {
+            TokenKind::Rbrace => {
                 brackets.pop();
             }
             _ => {}

crates/ruff_linter/src/rules/pycodestyle/snapshots/ruff_linter__rules__pycodestyle__tests__E203_E20.py.snap

@@ -251,6 +251,8 @@ E20.py:155:14: E203 [*] Whitespace before ':'
 154 | #: E203:1:13
 155 | ham[lower + 1  :, "columnname"]
     |              ^^ E203
+156 | 
+157 | #: Okay
     |
     = help: Remove whitespace before ':'
 
@@ -260,3 +262,21 @@ E20.py:155:14: E203 [*] Whitespace before ':'
 154 154 | #: E203:1:13
 155     |-ham[lower + 1  :, "columnname"]
     155 |+ham[lower + 1:, "columnname"]
+156 156 | 
+157 157 | #: Okay
+158 158 | f"{ham[lower +1 :, "columnname"]}"
+
+E20.py:161:17: E203 [*] Whitespace before ':'
+    |
+160 | #: E203:1:13
+161 | f"{ham[lower + 1  :, "columnname"]}"
+    |                 ^^ E203
+    |
+    = help: Remove whitespace before ':'
+
+ℹ Safe fix
+158 158 | f"{ham[lower +1 :, "columnname"]}"
+159 159 | 
+160 160 | #: E203:1:13
+161     |-f"{ham[lower + 1  :, "columnname"]}"
+    161 |+f"{ham[lower + 1:, "columnname"]}"