Created attachment 137143 [details]
Screenshot of the issue

If a 'cases' environment is inside a math environment, for example inside a 'gather' environment, after the 'cases' environment the math syntaxing/highlighting will stop for the test of the math environment

To reproduce, this is an example for it:
```
\begin{gather*}
    a = 5 \\
    y = \begin{cases}
      0 & x < 2 \\
      2x-4 & x > 2 \\
    \end{cases} \\
    x = 5 \\
    z = 5
  \end{gather*}
```
Where `x &= 5 \\` and `z &= 5` won't have the math syntaxing/highlighting applied to them even tough they should. I have attached a screenshot of it for demonstation

SOFTWARE/OS VERSIONS:
Operating System: Arch Linux
KDE Plasma Version: 5.21.3
KDE Frameworks Version: 5.80.0
Qt Version: 5.15.2
Kernel Version: 5.11.8-arch1-1
OS Type: 64-bit
Graphics Platform: X11