chore: upgrade to mui v6 (#267)

* chore: upgrade to mui v6

* chore: run pnpm dedupe

* Fix example project lock file (bumping mui and tss-react)

Note that this required also running the following inside the `example/` dir:

```
pnpm add [email protected]
pnpm dedupe
pnpm remove tss-react
pnpm i
```

in order to ensure that we were on a compatible version of tss-react
with mui v6 specified as our MUI dep. Otherwise:

```
 WARN  Issues with peer dependencies found
.
└─┬ mui-tiptap 1.10.0
  └─┬ tss-react 4.9.10
    └── ✕ unmet peer @mui/material@^5.0.0: found 6.0.1
```

(v6 support was added in 4.9.13 of tss-react
garronej/tss-react@d09cbfe)

---------

Co-authored-by: Steven DeMartini <[email protected]>

example/package.json

@@ -13,8 +13,8 @@
     "@emotion/react": "^11.11.0",
     "@emotion/styled": "^11.11.0",
     "@fontsource/roboto": "^4.5.8",
-    "@mui/icons-material": "^5.11.16",
-    "@mui/material": "^5.12.3",
+    "@mui/icons-material": "^6.0.1",
+    "@mui/material": "^6.0.1",
     "@tiptap/core": "2.0.3",
     "@tiptap/extension-blockquote": "2.0.3",
     "@tiptap/extension-bold": "2.0.3",