CHANGELOG formatting: fix heading levels

Revisions are level 2, so anything belonging to that level should be
level 3 or even lower priority.

CHANGELOG.md

@@ -23,7 +23,7 @@ This file was introduced starting Kani 0.23.0, so it only contains changes from
 * Delete obsolete stubs for `Vec` and related options by @zhassan-aws in https://github.com/model-checking/kani/pull/2770
 * Add support for the ARM64 Linux platform by @adpaco-aws in https://github.com/model-checking/kani/pull/2757
 
-## What's Changed
+### What's Changed
 
 * Function Contracts: Support for defining and checking `requires` and `ensures` clauses by @JustusAdam in https://github.com/model-checking/kani/pull/2655
 * Force `any_vec` capacity to match length by @celinval in https://github.com/model-checking/kani/pull/2765
@@ -36,7 +36,7 @@ This file was introduced starting Kani 0.23.0, so it only contains changes from
 
 ## [0.36.0]
 
-## What's Changed
+### What's Changed
 
 * Enable `-Z stubbing` and error out instead of ignoring stub by @celinval in https://github.com/model-checking/kani/pull/2678
 * Enable concrete playback for failure of UB checks by @zhassan-aws in https://github.com/model-checking/kani/pull/2727
@@ -47,7 +47,7 @@ This file was introduced starting Kani 0.23.0, so it only contains changes from
 
 ## [0.35.0]
 
-## What's Changed
+### What's Changed
 
 * Add support to `simd_bitmask` by @celinval in https://github.com/model-checking/kani/pull/2677
 * Add integer overflow checking for `simd_div` and `simd_rem` by @reisnera in https://github.com/model-checking/kani/pull/2645
@@ -64,7 +64,7 @@ By default, Kani will now run CBMC with CaDiCaL, since this solver has outperfor
 User's should still be able to select Minisat (or a different solver) either by using `#[solver]` harness attribute,
 or by passing `--solver=<SOLVER>` command line option.
 
-## What's Changed
+### What's Changed
 
 * Allow specifying the scheduling strategy in #[kani_proof] for async functions by @fzaiser in https://github.com/model-checking/kani/pull/1661
 * Support for stubbing out foreign functions by @feliperodri in https://github.com/model-checking/kani/pull/2658
@@ -79,7 +79,7 @@ or by passing `--solver=<SOLVER>` command line option.
 
 ## [0.33.0]
 
-## What's Changed
+### What's Changed
 * Add support for sysconf by @feliperodri in https://github.com/model-checking/kani/pull/2557
 * Print Kani version by @adpaco-aws in https://github.com/model-checking/kani/pull/2619
 * Upgrade Rust toolchain to nightly-2023-07-01 by @qinheping in https://github.com/model-checking/kani/pull/2616
@@ -89,7 +89,7 @@ or by passing `--solver=<SOLVER>` command line option.
 
 ## [0.32.0]
 
-## What's Changed
+### What's Changed
 
 * Add kani::spawn and an executor to the Kani library by @fzaiser in https://github.com/model-checking/kani/pull/1659
 * Add "kani" configuration key to enable conditional compilation in build scripts by @celinval in https://github.com/model-checking/kani/pull/2297
@@ -103,7 +103,7 @@ or by passing `--solver=<SOLVER>` command line option.
 
 ## [0.31.0]
 
-## What's Changed
+### What's Changed
 * Add `--exact` flag by @jaisnan in https://github.com/model-checking/kani/pull/2527
 * Build the verification libraries using Kani compiler by @celinval in https://github.com/model-checking/kani/pull/2534
 * Verify all Kani attributes in all crate items upfront by @celinval in https://github.com/model-checking/kani/pull/2536
@@ -114,7 +114,7 @@ or by passing `--solver=<SOLVER>` command line option.
 
 ## [0.30.0]
 
-## What's Changed
+### What's Changed
 * Remove --harness requirement from stubbing by @celinval in https://github.com/model-checking/kani/pull/2495
 * Add target selection for cargo kani by @celinval in https://github.com/model-checking/kani/pull/2507
 * Generate Multiple playback harnesses when multiple crashes exist in a single harness. by @YoshikiTakashima in https://github.com/model-checking/kani/pull/2496