deps: update dependency com.google.cloud:google-cloud-bigtable to v1.19.1 (googleapis#1025)

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This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [com.google.cloud:google-cloud-bigtable](https://togithub.com/googleapis/java-bigtable) | patch | `1.19.0` -> `1.19.1` |

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### Release Notes

<details>
<summary>googleapis/java-bigtable</summary>

### [`v1.19.1`](https://togithub.com/googleapis/java-bigtable/blob/master/CHANGELOG.md#&#8203;1191-httpswwwgithubcomgoogleapisjava-bigtablecomparev1190v1191-2020-12-14)

[Compare Source](https://togithub.com/googleapis/java-bigtable/compare/v1.19.0...v1.19.1)

</details>

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samples/install-without-bom/pom.xml

@@ -63,7 +63,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-bigtable</artifactId>
-      <version>1.19.0</version>
+      <version>1.19.1</version>
       <scope>test</scope>
     </dependency>
     <dependency>

samples/snapshot/pom.xml

@@ -61,7 +61,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-bigtable</artifactId>
-      <version>1.19.0</version>
+      <version>1.19.1</version>
       <scope>test</scope>
     </dependency>
     <dependency>

samples/snippets/pom.xml

@@ -76,7 +76,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-bigtable</artifactId>
-      <version>1.19.0</version>
+      <version>1.19.1</version>
       <scope>test</scope>
     </dependency>
     <dependency>