chore(config): migrate renovate config (#15501)

The Renovate config in this repository needs migrating. Typically this
is because one or more configuration options you are using have been
renamed.

You don't need to merge this PR right away, because Renovate will
continue to migrate these fields internally each time it runs. But later
some of these fields may be fully deprecated and the migrations removed.
So it's a good idea to merge this migration PR soon.

#### [PLEASE
NOTE](https://docs.renovatebot.com/configuration-options#configmigration):
JSON5 config file migrated! All comments & trailing commas were removed.

🔕 **Ignore**: Close this PR and you won't be reminded about config
migration again, but one day your current config may no longer be valid.

❓ Got questions? Does something look wrong to you? Please don't hesitate
to [request help
here](https://redirect.github.com/renovatebot/renovate/discussions).

---

This PR was generated by [Mend Renovate](https://mend.io/renovate/).
View the [repository job
log](https://developer.mend.io/github/rust-lang/cargo).

Author: ehuss

.github/renovate.json5

@@ -11,8 +11,8 @@
   customManagers: [
     {
       customType: 'regex',
-      fileMatch: [
-        'Cargo.toml$',
+      managerFilePatterns: [
+        '/Cargo.toml$/',
       ],
       matchStrings: [
         '\\bMSRV:1\\b.*?(?<currentValue>\\d+\\.\\d+(\\.\\d+)?)',
@@ -24,8 +24,8 @@
     },
     {
       customType: 'regex',
-      fileMatch: [
-        'Cargo.toml$',
+      managerFilePatterns: [
+        '/Cargo.toml$/',
       ],
       matchStrings: [
         '\\bMSRV:3\\b.*?(?<currentValue>\\d+\\.\\d+(\\.\\d+)?)',
@@ -37,8 +37,8 @@
     },
     {
       customType: 'regex',
-      fileMatch: [
-        '^.github.workflows.main.yml$',
+      managerFilePatterns: [
+        '/^.github.workflows.main.yml$/',
       ],
       matchStrings: [
         'cargo-semver-checks.releases.download.v(?<currentValue>\\d+\\.\\d+(\\.\\d+)?)',