Browser: crash with `is_monotonically_increasing()`

[flqwer]

1032.850 WebContent(184): VERIFICATION FAILED: is_monotonically_increasing() at ./Userland/Libraries/LibWeb/Animations/DocumentTimeline.cpp:67
1032.858 [WebContent(184:184)]: CRASH: CPU #0 Illegal instruction in userspace
1032.858 [#0 WebContent(184:184)]: Exception code: 0000 (isr: 0000)
1032.858 [#0 WebContent(184:184)]:     pc=0x0023:0x00000009770cb88d rflags=0x0000000000010206
1032.858 [#0 WebContent(184:184)]:  stack=0x00000012cf1e19f0  fs=0x000000000ce79000  gs=0x0000002009f9f018
1032.858 [#0 WebContent(184:184)]:    rax=0x0000000000000000 rbx=0x0000000d0e068160 rcx=0x0000000bad5f502b rdx=0x00000012cf1e1898
1032.858 [#0 WebContent(184:184)]:    rbp=0x00000012cf1e1a20 rsp=0x000000201439fee0 rsi=0x000000097718ab70 rdi=0x00000000000000a5
1032.858 [#0 WebContent(184:184)]:     r8=0x00000012cf1e1740  r9=0x000000000000000a r10=0x000000097718ab70 r11=0x0000000000000202
1032.858 [#0 WebContent(184:184)]:    r12=0x00000012cd9b4a40 r13=0x00000012cf1e1af0 r14=0x00000006c3ab07e0 r15=0x00000017329b5040
1032.858 [#0 WebContent(184:184)]:    cr0=0x0000000080010013 cr2=0x00000007613d6000 cr3=0x0000000050a54000 cr4=0x0000000000340ee0
1032.858 [#0 WebContent(184:184)]: 0x00000009770cb88d  (?)

1032.858 [#0 WebContent(184:184)]: Kernel backtrace:
Kernel + 0x00000000004ad5a1  Kernel::Process::crash(int, AK::Optional<Kernel::RegisterState const&>, bool) +0x1c1
Kernel + 0x000000000048c35a  Kernel::handle_crash(Kernel::RegisterState const&, char const*, int, bool) +0x65a
Kernel + 0x0000000000516670  illegal_instruction_asm_entry +0x30

Seems to happen with almost every somewhat-heavy site (tested on https://wallhaven.cc).

[spholz]

See also https://discord.com/channels/830522505605283862/830525031720943627/1425600350982901890

We need to cherry-pick LadybirdBrowser/ladybird#5636, but that would require fixups for LibGC. In general, it's probably better to wait for previous PRs to be cherry-picked to not create further conflicts in that code.