fix typos (flutter#7912)

Fix a few typos.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [ ] I listed at least one issue that this PR fixes in the description
above.
- [ ] I updated/added relevant documentation (doc comments with `///`).
- [ ] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] All existing and new tests are passing.

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Author: pq

CONTRIBUTING.md

@@ -54,7 +54,7 @@ name and contact info to the [AUTHORS](AUTHORS) file.
 
 ## Setting environments
 
-The current Java Developmenet Kit version is: **20**.
+The current Java Development Kit version is: **20**.
 
 1. Set your `JAVA_HOME` directory in your environment.
     - For example, on macOS, the following works:
@@ -75,7 +75,7 @@ The current Java Developmenet Kit version is: **20**.
    export PATH=$DART_SDK/bin:$FLUTTER_SDK/bin:$JAVA_HOME/bin:$PATH
    ```
 5. Make sure you're using the latest stable release of IntelliJ,
-   or sownload and install the latest version of IntelliJ (2023.1 or later).
+   or download and install the latest version of IntelliJ (2023.1 or later).
     - [IntelliJ Downloads](https://www.jetbrains.com/idea/download/)
     - Either the community edition (free) or Ultimate will work.
     - Determine the directory of your downloaded IntelliJ IDEA installation. e.g.