docs(panel): fix ampersands getting parsed into &amp; (#11450)
docs(panel): fix ampersands getting parsed into &amp; (#11450)

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## PR Checklist
Please check that your PR fulfills the following requirements:
- [x] The commit message follows [our guidelines](https://github.com/angular/material/blob/master/.github/CONTRIBUTING.md#-commit-message-format)
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## PR Type
What kind of change does this PR introduce?
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[ ] Bugfix
[ ] Enhancement
[x] Documentation content changes
[ ] Code style update (formatting, local variables)
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## What is the current behavior?
Some of the code in the example was getting parsed to `&amp;&amp;`.
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Issue Number: 
N/A

## What is the new behavior?
Fixed to not use `&&` in this example.

## Does this PR introduce a breaking change?
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[ ] Yes
[x] No
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## Other information

Splaktar/material,angular/material,bluebirdtech/material,marekmicek/material,oostmeijer/material,angular/material,marekmicek/material,marekmicek/material,bluebirdtech/material,clshortfuse/material,marekmicek/material,clshortfuse/material,miguelcobain/material,Splaktar/material,Splaktar/material,bluebirdtech/material,bluebirdtech/material,Splaktar/material,clshortfuse/material,oostmeijer/material,oostmeijer/material,miguelcobain/material,oostmeijer/material,miguelcobain/material,clshortfuse/material,angular/material,angular/material,miguelcobain/material