MQE: fix issue where rate or increase can return multiple series with the same labels

[charleskorn]

What this PR does

This PR fixes an issue in MQE's implementation of rate and increase that can cause it to return multiple series with the same labels instead of a single series or returning a vector cannot contain metrics with the same labelset error.

I have a more robust fix planned: moving NeedsSeriesDeduplication to a new SeriesMetadataFunc struct, so that NeedsSeriesDeduplication is always true for DropSeriesName, but I'd like to merge this simpler fix first as it will be far easier to backport.

Which issue(s) this PR fixes or relates to

(none)

Checklist

• Tests updated.
• [n/a] Documentation added.
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• [n/a] about-versioning.md updated with experimental features.

[grafanabot]

The backport to r309 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-9553-to-r309 origin/r309
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 25dadff171ce4edc9376c7b536f5fa39dbc2519d
# Push it to GitHub
git push --set-upstream origin backport-9553-to-r309
git switch main
# Remove the local backport branch
git branch -D backport-9553-to-r309

Then, create a pull request where the base branch is r309 and the compare/head branch is backport-9553-to-r309.

[grafanabot]

The backport to r308 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-9553-to-r308 origin/r308
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 25dadff171ce4edc9376c7b536f5fa39dbc2519d
# Push it to GitHub
git push --set-upstream origin backport-9553-to-r308
git switch main
# Remove the local backport branch
git branch -D backport-9553-to-r308

Then, create a pull request where the base branch is r308 and the compare/head branch is backport-9553-to-r308.

[grafanabot]

The backport to r310 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-9553-to-r310 origin/r310
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 25dadff171ce4edc9376c7b536f5fa39dbc2519d
# Push it to GitHub
git push --set-upstream origin backport-9553-to-r310
git switch main
# Remove the local backport branch
git branch -D backport-9553-to-r310

Then, create a pull request where the base branch is r310 and the compare/head branch is backport-9553-to-r310.

[grafanabot]

The backport to r311 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-9553-to-r311 origin/r311
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 25dadff171ce4edc9376c7b536f5fa39dbc2519d
# Push it to GitHub
git push --set-upstream origin backport-9553-to-r311
git switch main
# Remove the local backport branch
git branch -D backport-9553-to-r311

Then, create a pull request where the base branch is r311 and the compare/head branch is backport-9553-to-r311.