Fix typos in pdfminer and pymupdf documentations (#30513)

This pull request includes fixes in documentation for PDF loaders to
correct the names of the loaders and the required installations. The
most important changes include updating the loader names and
installation instructions in the Jupyter notebooks.

Documentation fixes:

*
[`docs/docs/integrations/document_loaders/pdfminer.ipynb`](diffhunk://#diff-a4a0561cd4a6e876ea34b7182de64a452060b921bb32d37b02e6a7980a41729bL34-R34):
Changed references from `PyMuPDFLoader` to `PDFMinerLoader` and updated
the installation instructions to replace `pymupdf` with `pdfminer`.
[[1]](diffhunk://#diff-a4a0561cd4a6e876ea34b7182de64a452060b921bb32d37b02e6a7980a41729bL34-R34)
[[2]](diffhunk://#diff-a4a0561cd4a6e876ea34b7182de64a452060b921bb32d37b02e6a7980a41729bL63-R63)
[[3]](diffhunk://#diff-a4a0561cd4a6e876ea34b7182de64a452060b921bb32d37b02e6a7980a41729bL330-R330)

*
[`docs/docs/integrations/document_loaders/pymupdf.ipynb`](diffhunk://#diff-8487995f457e33daa2a08fdcff3b42e144eca069eeadfad5651c7c08cce7a5cdL292-R292):
Corrected the loader name from `PDFPlumberLoader` to `PyMuPDFLoader`.

docs/docs/integrations/document_loaders/pdfminer.ipynb

@@ -31,7 +31,7 @@
     "\n",
     "### Credentials\n",
     "\n",
-    "No credentials are required to use PyMuPDFLoader"
+    "No credentials are required to use PDFMinerLoader"
    ]
   },
   {
@@ -60,7 +60,7 @@
    "source": [
     "### Installation\n",
     "\n",
-    "Install **langchain_community** and **pymupdf**."
+    "Install **langchain_community** and **pdfminer**."
    ]
   },
   {
@@ -327,7 +327,7 @@
     "- By page\n",
     "- As a single text flow\n",
     "\n",
-    "By default PDFPlumberLoader will split the PDF by page."
+    "By default PDFMinerLoader will split the PDF by page."
    ]
   },
   {

docs/docs/integrations/document_loaders/pymupdf.ipynb

@@ -289,7 +289,7 @@
     "- By page\n",
     "- As a single text flow\n",
     "\n",
-    "By default PDFPlumberLoader will split the PDF by page."
+    "By default PyMuPDFLoader will split the PDF by page."
    ]
   },
   {