build(deps): update dependency org.apache.maven.plugins:maven-failsafe-plugin to v3.0.0-m6 (#1801)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [org.apache.maven.plugins:maven-failsafe-plugin](https://maven.apache.org/surefire/) | `3.0.0-M5` -> `3.0.0-M6` | [![age](https://badges.renovateapi.com/packages/maven/org.apache.maven.plugins:maven-failsafe-plugin/3.0.0-M6/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/org.apache.maven.plugins:maven-failsafe-plugin/3.0.0-M6/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/org.apache.maven.plugins:maven-failsafe-plugin/3.0.0-M6/compatibility-slim/3.0.0-M5)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/org.apache.maven.plugins:maven-failsafe-plugin/3.0.0-M6/confidence-slim/3.0.0-M5)](https://docs.renovatebot.com/merge-confidence/) |

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samples/install-without-bom/pom.xml

@@ -139,7 +139,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-failsafe-plugin</artifactId>
-        <version>3.0.0-M5</version>
+        <version>3.0.0-M6</version>
         <configuration>
           <systemPropertyVariables>
             <spanner.test.instance>spanner-testing-east1</spanner.test.instance>

samples/snapshot/pom.xml

@@ -138,7 +138,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-failsafe-plugin</artifactId>
-        <version>3.0.0-M5</version>
+        <version>3.0.0-M6</version>
         <configuration>
           <systemPropertyVariables>
             <spanner.test.instance>spanner-testing-east1</spanner.test.instance>

samples/snippets/pom.xml

@@ -143,7 +143,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-failsafe-plugin</artifactId>
-        <version>3.0.0-M5</version>
+        <version>3.0.0-M6</version>
         <configuration>
           <systemPropertyVariables>
             <spanner.test.instance>spanner-testing-east1</spanner.test.instance>