Update UI tests which relied on old behavior of constructing a default error handler every time

`early_warn` is called

Skip `colored-session-opt-error.rs` on Windows hosts

This is very cursed as to why it fails on Windows CI specifically:

- The test emits a *warning*.
- *Warnings*, and only warnings *specifically*, have a different
  256-color between Windows and non-Windows hosts (other levels
  `set_intense(true)` unconditionally):

  e69c7306e2/compiler/rustc_errors/src/lib.rs (L1792-L1794)

Therefore, I added `// ignore-windows` test header to skip this test on
Windows (it's sufficient to test color is enabled on at least one
non-Windows host).

tests/ui/conditional-compilation/cfg-arg-invalid-1.rs

@@ -1,3 +1,3 @@
-// compile-flags: --cfg a(b=c)
+// compile-flags: --error-format=human --cfg a(b=c)
 // error-pattern: invalid `--cfg` argument: `a(b=c)` (expected `key` or `key="value"`, ensure escaping is appropriate for your shell, try 'key="value"' or key=\"value\")
 fn main() {}

tests/ui/conditional-compilation/cfg-arg-invalid-2.rs

@@ -1,3 +1,3 @@
-// compile-flags: --cfg a{b}
+// compile-flags: --error-format=human --cfg a{b}
 // error-pattern: invalid `--cfg` argument: `a{b}` (expected `key` or `key="value"`)
 fn main() {}

tests/ui/conditional-compilation/cfg-arg-invalid-4.rs

@@ -1,3 +1,3 @@
-// compile-flags: --cfg a(b)
+// compile-flags: --error-format=human --cfg a(b)
 // error-pattern: invalid `--cfg` argument: `a(b)` (expected `key` or `key="value"`)
 fn main() {}

tests/ui/conditional-compilation/cfg-arg-invalid-6.rs

@@ -1,3 +1,3 @@
-// compile-flags: --cfg a{
+// compile-flags: --error-format=human --cfg a{
 // error-pattern: invalid `--cfg` argument: `a{` (expected `key` or `key="value"`)
 fn main() {}

tests/ui/conditional-compilation/cfg-arg-invalid-8.rs

@@ -1,3 +1,3 @@
-// compile-flags: --cfg )
+// compile-flags: --error-format=human --cfg )
 // error-pattern: invalid `--cfg` argument: `)` (expected `key` or `key="value"`)
 fn main() {}

tests/ui/conditional-compilation/cfg-arg-invalid-9.rs

@@ -1,4 +1,4 @@
 // Test for missing quotes around value, issue #66450.
-// compile-flags: --cfg key=value
+// compile-flags: --error-format=human --cfg key=value
 // error-pattern: invalid `--cfg` argument: `key=value` (expected `key` or `key="value"`, ensure escaping is appropriate for your shell, try 'key="value"' or key=\"value\")
 fn main() {}

tests/ui/conditional-compilation/cfg-empty-codemap.rs

@@ -1,6 +1,6 @@
 // Tests that empty source_maps don't ICE (#23301)
 
-// compile-flags: --cfg ""
+// compile-flags: --error-format=human --cfg ""
 
 // error-pattern: invalid `--cfg` argument: `""` (expected `key` or `key="value"`)
 

tests/ui/diagnostic-flags/colored-session-opt-error.rs

@@ -1,3 +1,4 @@
 // check-pass
+// ignore-windows
 // compile-flags: -Cremark=foo --error-format=human --color always
 fn main() {}