docs: revert string formatting change of "jj help util exec"

Appears that "cargo test" parses indented text as a code block, and fails to
run doc tests. Spotted by running "cargo insta test". This doc comment is a CLI
help which is usually rendered to console, so I think markdown annotation should
be minimal.

This backs out commit ed84468, "docs: in `jj help util exec`, use Markdown
`warning` admonition."

cli/src/commands/util/exec.rs

@@ -22,13 +22,13 @@ use crate::ui::Ui;
 ///
 /// This is useful for arbitrary aliases.
 ///
-/// !!! warning
+/// !! WARNING !!
 ///
-///     The following technique just provides a convenient syntax for running
-///     arbitrary code on your system. Using it irresponsibly may cause damage
-///     ranging from breaking the behavior of `jj undo` to wiping your file
-///     system.  Exercise the same amount of caution while writing these aliases
-///     as you would when typing commands into the terminal!
+/// The following technique just provides a convenient syntax for running
+/// arbitrary code on your system. Using it irresponsibly may cause damage
+/// ranging from breaking the behavior of `jj undo` to wiping your file system.
+/// Exercise the same amount of caution while writing these aliases as you would
+/// when typing commands into the terminal!
 ///
 /// This feature may be removed or replaced by an embedded scripting language in
 /// the future.

cli/tests/cli-reference@.md.snap

@@ -1,6 +1,7 @@
 ---
 source: cli/tests/test_generate_md_cli_help.rs
 description: "AUTO-GENERATED FILE, DO NOT EDIT. This cli reference is generated by a test as an `insta` snapshot. MkDocs includes this snapshot from docs/cli-reference.md."
+snapshot_kind: text
 ---
 <!-- BEGIN MARKDOWN-->
 
@@ -2214,13 +2215,13 @@ Execute an external command via jj
 
 This is useful for arbitrary aliases.
 
-!!! warning
+!! WARNING !!
 
-    The following technique just provides a convenient syntax for running
-    arbitrary code on your system. Using it irresponsibly may cause damage
-    ranging from breaking the behavior of `jj undo` to wiping your file
-    system.  Exercise the same amount of caution while writing these aliases
-    as you would when typing commands into the terminal!
+The following technique just provides a convenient syntax for running
+arbitrary code on your system. Using it irresponsibly may cause damage
+ranging from breaking the behavior of `jj undo` to wiping your file system.
+Exercise the same amount of caution while writing these aliases as you would
+when typing commands into the terminal!
 
 This feature may be removed or replaced by an embedded scripting language in
 the future.